Three-dimensional net-like aluminum porous body, electrode using the aluminum porous body, nonaqueous electrolyte battery using the electrode, and nonaqueous electrolyte capacitor using the electrode

ABSTRACT

Provided are a three-dimensional net-like aluminum porous body in which the diameter of cells in the porous body is uneven in the thickness direction of the porous body; a current collector and an electrode each using the aluminum porous body; and methods for producing these members. The porous body is a three-dimensional net-like aluminum porous body in a sheet form, for a current collector, in which the diameter of cells in the porous body is uneven in the thickness direction of the porous body. When a cross section in the thickness direction of the three-dimensional net-like aluminum porous body is divided into three regions of a region  1 , a region  2  and a region  3  in this order, the average cell diameter of the regions  1  and  3  is preferably different from the cell diameter of the region  2.

TECHNICAL FIELD

The present invention relates to a three-dimensional net-like aluminumporous body used as an electrode for a nonaqueous electrolyte battery(such as a lithium battery), a capacitor using a nonaqueous electrolyte,which may be referred to as a “capacitor” hereinafter, or some otherarticle.

BACKGROUND ART

Metallic porous bodies having a three-dimensional net-like structure areused in the fields of various articles, such as various filters,catalyst carriers, and electrodes for batteries. For example, CELMET((registered trade mark) manufactured by Sumitomo Electric Industries,Ltd.), which is made of a three-dimensional net-like nickel porous body(hereinafter referred to as a “nickel porous body”), is used as amaterial for an electrode of a battery such as a nickel hydrogen batteryor a nickel cadmium battery. The CELMET is a metallic porous body havingcontinuous pores, and is characterized by having a higher porosity (90%or more) than other porous bodies such as a metallic nonwoven fabric.This is obtained by forming a nickel layer onto the surface of askeleton of a resin porous body having continuous pores, such as aurethane foam, treating the workpiece thermally to decompose the resinfoam shaped body, and further reducing the nickel. The formation of thenickel layer is attained by painting a carbon powder or some other ontothe skeleton surface of the resin foam shaped body to subject thesurface to an electrically conduction treatment, and then electroplatingthe workpiece to precipitate nickel.

In the meantime, aluminum has excellent characteristics, such aselectroconductivity, corrosion resistance and lightness, similarly tonickel. About the use thereof for batteries, the following is used as apositive electrode of a lithium battery: a member in which an activematerial such as lithium cobaltate is painted on surfaces of an aluminumfoil. In order to improve the capacity of the positive electrode, it isconceived that a three-dimensional net-like aluminum porous body(hereinafter referred to as an “aluminum porous body”), wherein thesurface area of the aluminum is made large, is used, and an activematerial is filled also into the aluminum. According to this form, theactive material can be used even when the electrode is made thick, sothat the electrode is improved in availability ratio of the activematerial per unit area.

As a method for producing an aluminum porous body, Patent Literature 1describes a method of subjecting a three-dimensional net-like plasticbase having internal spaces connected to each other to an aluminum vapordeposition treatment by an arc ion plating method, thereby forming ametallic aluminum layer of 2 to 20 μm thickness.

It is stated that according to this method, an aluminum porous body of 2to 20 μm thickness is obtained; however, the porous body is not easilyproduced so as to have a large area since the method is based on a vapordeposition method. Depending on the thickness or the porosity of thebase, the layer is not easily formed so as to be even inside the porousbody. Moreover, the forming velocity of the aluminum layer is small;costs for the production increase because of a high price of facilities,and other causes; and other problems remain. Furthermore, when aluminumis made into a thick film, it is feared that the film is cracked oraluminum peels off.

Patent Literature 2 describes a method of yielding an aluminum porousbody by forming a film made of a metal (such as copper) capable ofproducing a eutectic alloy at the melting point of aluminum, or loweronto a skeleton of a resin foam shaped body having a three-dimensionalnet-like structure, painting an aluminum paste thereon, and treating theworkpiece thermally at a temperature of 550° C. or higher and 750° C. orlower in a non-oxidizing atmosphere, thereby removing the organiccomponent (the resin foam) and sintering the aluminum powder.

However, according to this method, a layer that is combined withaluminum to form a eutectic alloy is unfavorably formed, so that analuminum layer high in purity cannot be formed.

In a different method, it is conceived that a resin foam shaped bodyhaving a three-dimensional net-like structure is plated with aluminum.The method of electroplating with aluminum is itself known. However, inplating with aluminum, the affinity of aluminum with oxygen is large,and the potential thereof is lower than that of hydrogen; thus, it isdifficult that electroplating therewith is conducted in a plating bathof an aqueous solution type. For this reason, about electroplating withaluminum, nonaqueous solution baths for plating have been hithertoinvestigated. For example, as a technique for plating a metal surfacewith aluminum in order to prevent the surface from being oxidized,Patent Literature 3 discloses an aluminum electroplating method of usinga low-melting-point composition wherein an onium halide and an aluminumhalide are mixed with each other and molten, as a plating bath, toprecipitate aluminum onto a negative electrode while the water contentin the bath is kept into 2% by weight or less.

However, about electroplating with aluminum, only a metal surface can beplated. There has not been known a method of electroplating a resinshaped body surface therewith, in particular, a method of electroplatinga surface of a resin porous body having a three-dimensional net-likestructure therewith.

CITATION LIST Patent Literatures

Patent Literature 1: Japanese Patent No. 3413662

Patent Literature 2: Japanese Unexamined Patent Publication No. 8-170126

Patent Literature 3: Japanese Patent No. 3202072

Patent Literature 4: Japanese Unexamined Patent Publication No. 56-86459

SUMMARY OF INVENTION Technical Problem

The present invention provides a practical technique for producing anelectrode industrially from an aluminum porous body. Specifically, anobject thereof is to provide a three-dimensional net-like aluminumporous body in which the diameter of cells in the porous body is unevenin the thickness direction of the porous body, a current collector andan electrode each using the aluminum porous body, and methods forproducing these members.

Solution to Problem

The inventors have made eager investigations about methods forelectroplating a surface of a urethane resin porous body having athree-dimensional net-like structure with aluminum to find out that suchplating can be attained by plating, with aluminum in a molten salt bath,a urethane resin porous body having at least a surface made electricallyconductive. Thus, a method for producing an aluminum porous body hasbeen completed. This production method makes it possible to yield analuminum structural body having a urethane resin porous body as askeleton core. Depending on an article in which the resultant porousbody is used, such as a filter that may be of various types, or acatalyst carrier, the resultant porous body may be used, as it is, as acomplex composed of the resin and the metal. However, when the resultantporous body is to be used as a metallic structural body containing noresin because of a restriction based on the use environment, and others,it is necessary to remove the resin to change the resultant porous bodyto an aluminum porous body.

The removal of the resin may be attained by using an organic solvent, amolten salt or supercritical water to decompose (dissolve) the resin, bythermally decomposing the resin, or by any other method.

The thermal decomposition method, or some other method at hightemperature is simple and easy while the method accompanies theoxidation of aluminum. Once aluminum is oxidized, the metal is noteasily reduced, this situation being different from that of nickel orthe like. Thus, when aluminum is used as a material for an electrode ofa battery or some other member, aluminum is oxidized to loseelectroconductivity. Thus, the metal cannot be used. Therefore, as amethod for removing a resin in such a manner that the aluminum is notoxidized, the inventors have completed a method in which in the statethat an aluminum structural body obtained by forming an aluminum layeron the surface of a porous resin shaped body is immersed in a moltensalt, the structural body is heated up to the melting point of aluminumor lower while a negative potential is applied to the aluminum layer, soas to decompose the porous resin shaped body thermally to be removed,thereby producing an aluminum porous body.

In order to use an aluminum porous body obtained as described above asan electrode, it is necessary to attach, through a process asillustrated in FIG. 1, lead wires to the aluminum porous body to preparea current collector, fill an active material into this aluminum porousbody as the current collector, and then subject the workpiece tocompression, cutting and some other processing. However, there has notyet been known any technique put into practical use for producingindustrially an electrode of a nonaqueous electrolyte battery, acapacitor wherein a nonaqueous electrolyte is used, or some otherarticle from the aluminum porous body.

The present invention is as follows:

(1) A three-dimensional net-like aluminum porous body in a sheet form,for a current collector, wherein the diameter of cells in the porousbody is uneven in the thickness direction of the porous body.

(2) The three-dimensional net-like aluminum porous body according toitem (1), wherein when a cross section in the thickness direction of theporous body is divided into three regions of a region 1, a region 2 anda region 3 in this order, the average cell diameter of the cell diameterof the region 1 and that of the region 3 is different from the celldiameter of the region 2.

(3) The three-dimensional net-like aluminum porous body according toitem (2), wherein the ratio of the average cell diameter of the celldiameter of the region 1 and that of the region 3 to the cell diameterof the region 2 is 1.1 or more.

(4) The three-dimensional net-like aluminum porous body according toitem (2), wherein the ratio of the average cell diameter of the celldiameter of the region 1 and that of the region 3 to the cell diameterof the region 2 is 0.9 or less.

(5) The three-dimensional net-like aluminum porous body according toitem (1), wherein when a cross section in the thickness direction of theporous body is divided into two regions of a region 4 and a region 5,the ratio of the cell diameter of the region 4 to that of the region 5is 1.1 or more.

(6) The three-dimensional net-like aluminum porous body according toitem (1), wherein three sheet-form aluminum porous bodies A, B and C arelaminated in this order onto each other in the respective thicknessdirections of the porous bodies to be integrated with each other, and

the ratio of the average cell diameter of the cell diameter of thealuminum porous body A and that of the aluminum porous body C to thecell diameter of the aluminum porous body B is 1.1 or more.

(7) The three-dimensional net-like aluminum porous body according toitem (1), wherein three sheet-form aluminum porous bodies D, E and F arelaminated in this order onto each other in the respective thicknessdirections of the porous bodies to be integrated with each other, and

the ratio of the average cell diameter of the cell diameter of thealuminum porous body D and that of the aluminum porous body F to thecell diameter of the aluminum porous body E is 0.9 or less.

(8) The three-dimensional net-like aluminum porous body according toitem (1), wherein two sheet-form aluminum porous bodies G and H arelaminated in this order onto each other in the respective thicknessdirections of the porous bodies to be integrated with each other, and

the ratio of the cell diameter of the aluminum porous body G to the celldiameter of the aluminum porous body H is 1.1 or more.

(9) The three-dimensional net-like aluminum porous body according toitem (1), wherein the oxygen content in a surface of the porous body is3.1% by mass or less.

(10) The three-dimensional net-like aluminum porous body according toitem (1), wherein when the porous body is divided in the thicknessdirection thereof into a large-cell-diameter region having a large celldiameter and a small-cell-diameter region having a smaller cell diameterthan this large cell diameter, the cell diameter of thelarge-cell-diameter region is 300 μm or more and 600 μm or less.

(11) The three-dimensional net-like aluminum porous body according toitem (1), wherein when the porous body is divided in the thicknessdirection thereof into a large-cell-diameter region having a large celldiameter and a small-cell-diameter region having a smaller cell diameterthan this large cell diameter, the cell diameter of thesmall-cell-diameter region is 50 μm or more and 300 μm or less.

(12) The three-dimensional net-like aluminum porous body according toitem (1), wherein when the porous body is divided in the thicknessdirection thereof into a large-cell-diameter region having a large celldiameter and a small-cell-diameter region having a smaller cell diameterthan this large cell diameter, the cell diameter of thesmall-cell-diameter region is less than 750 μm.

(13) An electrode wherein the three-dimensional net-like aluminum porousbody as recited in any one of items (1) to (12) is used.

(14) A nonaqueous electrolyte battery wherein the electrode as recitedin item (13) is used.

(15) A capacitor using a nonaqueous electrolyte wherein the electrode asrecited in item (13) is used.

Advantageous Effects of Invention

The three-dimensional net-like aluminum porous body according to thepresent invention can be used in a process for producing electrodematerials continuously, and makes it possible to lower industrial costsfor the production.

When the three-dimensional net-like aluminum porous body of the presentinvention is used as a base of an electrode, the porous body can makeimprovements of the electrode in current collecting performance of acentral region in the thickness direction thereof and in availabilityratio of the active material inside the electrode. Furthermore, theporous body can make improvements of the electrode in holdingperformance of the active material, battery lifespan, and windability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a process for producing an electrodematerial from an aluminum porous body.

FIG. 2 is a schematic sectional view illustrating an aluminum porousbody wherein an inner region (central region) is smaller in celldiameter than outer surface regions (the front and rear surfaces).

FIG. 3 is a schematic sectional view illustrating an aluminum porousbody wherein outer surface regions (the front and rear surfaces) aresmaller in cell diameter than an inner region (central region).

FIG. 4 is a schematic sectional view illustrating an aluminum porousbody wherein one of both half sides in the thickness direction is largerin cell diameter than the other half side.

FIG. 5 is a schematic sectional view illustrating two types of aluminumporous bodies having different cell diameters.

FIG. 6 is a flowchart showing a process for producing an aluminumstructural body according to the present invention.

FIG. 7A is an enlarged schematic view of an example resin porous bodybase wherein a surface of the resin porous body having continuous poresis enlarged.

FIG. 7B illustrates a conductive layer thinly formed on a surface of theresin porous body.

FIG. 7C illustrates an aluminum plating layer on a surface of theconductive layer formed on the resin porous body.

FIG. 7D illustrates a porous aluminum structural body in which only themetal layer remains after removal of the resin porous body.

FIG. 8 is a surface enlarged photograph showing the structure of aurethane resin porous body.

FIG. 9 is a view illustrating an example of a continuous aluminumplating step according to plating with a molten salt.

FIG. 10 is a view illustrating the step of compressing an end of analuminum porous body to form a compressed region.

FIG. 11 is a view illustrating the step of compressing a central regionof an aluminum porous body to form a compressed region.

FIG. 12 is a view illustrating the step of filling an active materialslurry into pores in an aluminum porous body.

FIG. 13 is a schematic view illustrating an example of a structurewherein an aluminum porous body is applied to a lithium battery.

FIG. 14 is a schematic view illustrating an example of a structurewherein an aluminum porous body is applied to a capacitor using anonaqueous electrolyte.

FIG. 15 is a schematic sectional view illustrating an example of astructure wherein an aluminum porous body is applied to a molten saltbattery.

DESCRIPTION OF EMBODIMENTS

The three-dimensional net-like aluminum porous body according to thepresent invention is a three-dimensional net-like aluminum porous bodyin a sheet form, for a current collector, wherein the diameter of cellsin the porous body is uneven in the thickness direction of the porousbody. In the present invention, it is preferred that when a crosssection in the thickness direction of the three-dimensional net-likealuminum porous body is divided into three regions of a region 1, aregion 2 and a region 3 in this order, the average of the cell diametersof the region 1 and the region 3 is different from the cell diameter ofthe region 2.

In the present invention, the cell diameter (pore diameter) of each ofthe regions in the cross section in the thickness direction of thealuminum porous body may be measured as follows:

A resin is first filled into portions of openings in thethree-dimensional net-like aluminum porous body. Examples of the filledresin include an epoxy resin, an acrylic resin, and a polyester resin.After the resin is solidified, the porous body is polished to create across section thereof. The cross section is observed with a microscope,and a photograph thereof is taken. Subsequently, the photograph isdivided into three regions in the thickness direction of the aluminumporous body. The regions are in turn named the region 1, the region 2and the region 3. The total number of skeleton ribs (i.e., the totalnumber of aluminum portions) contained in each of the regions in thephotograph is counted. This measurement is made about each of fivedifferent cross sections, and the average thereof is calculated out.

The reciprocal of this number of the skeleton ribs is in proportion tothe cell diameter; thus, in the present invention, a discussion will bemade by use of the reciprocal of the number of the skeleton ribs.

As described above, the three-dimensional net-like aluminum porous bodyof the present invention is characterized in that the cell diameter(pore diameter) is uneven in the thickness direction. It can beconceived that the three-dimensional net-like aluminum porous bodyhaving this structure is classified into, for example, the followingthree embodiments [1] to [3]:

[1] As illustrated in FIG. 2, an embodiment wherein an inner region (thecentral region) of the sheet-form aluminum porous body is made small incell diameter, and outer surface regions (the front surface and the rearsurface) thereof are made large in cell diameter;

[2] As illustrated in FIG. 3, an embodiment wherein outer surfaceregions (the front surface and the rear surface) of the sheet-formaluminum porous body are made small in cell diameter, and an innerregion (the central region) thereof is made large in cell diameter; and

[3] As illustrated in FIG. 4, an embodiment wherein one of both halfsides in the thickness direction of the sheet-form aluminum porous bodyis made smaller in cell diameter than the other half side.

The following will describe a specific configuration of each of theembodiments [1] to [3], and effects thereof.

Re: Embodiment [1]

When an aluminum porous body is used as the base of an electrode of anonaqueous electrolyte battery (such as a lithium battery), a capacitorwherein a nonaqueous electrolyte is used, or some other article, in aregion of the porous body where the diameter of cells is small, thedistance between the active material and the skeleton is small.Therefore, in the case of using, as the base of an electrode, athree-dimensional net-like aluminum porous body of the embodiment [1] asillustrated in FIG. 2, the electrode is improved in current collectingperformance and availability ratio of the active material inside acentral region in the thickness direction thereof. Thus, the providedelectrode can be an electrode excellent in power characteristic.

For this reason, in the three-dimensional net-like aluminum porous bodyof the present invention, the ratio of the average of the cell diametersof the region 1 and the region 3 to the cell diameter of the region 2 ispreferably 1.1 or more, more preferably 1.5 or more. If the ratio of theaverage cell diameter of the regions 1 and 3 to the cell diameter of theregion 2 is less than 1.1, it is difficult for the porous body to obtainthe above-mentioned effects of the improvements in current collectingperformance and availability ratio of the active material of the centralregion in the thickness direction.

As described above, this ratio between the cell diameters is obtained bycounting the number of the skeleton ribs from a microscopic photographof each of the regions, gaining the respective reciprocals of theresultant numbers, and calculating the ratio between these numericalvalues. In other words, a calculation is made about the average of thereciprocal value of the number of the skeleton ribs of the region 1(hereinafter, the reciprocal value of the number of skeleton ribs may bereferred to merely as the reciprocal value) and the reciprocal value ofthe region 3, and then this is divided by the reciprocal value of theregion 2.

In order to produce an aluminum porous body wherein the ratio of theaverage of the cell diameters of the regions 1 and 3 to the celldiameter of the region 2 is 1.1 or more as described above, apolyurethane foam as described in the following is used in an aluminumporous body-producing process which will be described later. That is, inthe step of foaming a polyurethane, at the time of foaming a foaming rawmaterial thereof continuously in a sheet-form mold, the upper and lowerplanes of the mold are warmed to 50° C. or higher, whereby the growth ofcells in the upper and lower planes of the sheet is promoted to give aurethane sheet having a desired cell diameter distribution in thethickness direction thereof. This urethane sheet is plated withaluminum, and the urethane is removed to yield the aluminum porous body,wherein the ratio of the average of the cell diameters of the regions 1and 3 to the cell diameter of the region 2 is 1.1 or more.

Aluminum porous bodies different from each other in cell diameter arelaminated onto each other, whereby the same effects can be produced. Inother words, the three-dimensional net-like aluminum porous body of thepresent invention is preferably a three-dimensional net-like aluminumporous body wherein three sheet-form aluminum porous bodies A, B and Care laminated in this order onto each other in the respective thicknessdirections of the porous bodies to be integrated with each other, andthe ratio of the average cell diameter of the aluminum porous bodies Aand C to the cell diameter of the aluminum porous body B is 1.1 or more.

Specifically, as illustrated in FIG. 5, prepared are two aluminum porousbody species, i.e., aluminum porous bodies small in cell diameter, andaluminum porous bodies large in cell diameter. One B of the aluminumporous bodies small in cell diameter is sandwiched between two A and Cof the aluminum porous bodies large in cell diameter so that thealuminum porous bodies are laminated onto each other to be integratedwith each other. This manner makes it possible to produce athree-dimensional net-like aluminum porous body wherein outer surfacelayer regions (the front surface and the rear surface) are large in celldiameter, and in reverse an inner region (the central layer region) issmall in cell diameter. The lamination and integration of the pluralaluminum porous bodies makes it possible to make the three-dimensionalnet-like aluminum porous body larger in thickness than ones in the priorart.

Additionally, the aluminum porous bodies A to C are selected to set, to1.1 or more, the ratio of the average cell diameter of the cell diameterof the aluminum porous body A and that of the aluminum porous body C tothe cell diameter of the aluminum porous body B, thereby making itpossible to improve the current collecting performance of the centralregion in the thickness direction of the resultant aluminum porous body,and further improve the availability ratio of the active material. Theratio of the average cell diameter of the aluminum porous bodies A and Cto the cell diameter of the aluminum porous body B is more preferably1.5 or more.

The manner for integrating the laminated aluminum porous bodies A to Cis not particularly limited. For example, the temperature of thelaminated aluminum porous body sheets is raised up to a temperatureclose to the melting point of aluminum in the state that pressure isapplied to the laminated sheets, whereby their skeletons contacting witheach other are melted to be bonded to each other so that the integrationcan be attained. Alternatively, the integration may be attained bybonding surfaces of the laminated aluminum porous bodies to each otherby welding such as spot welding.

Re: Embodiment [2]

As described above, when an aluminum porous body is used as the base ofan electrode of a nonaqueous electrolyte battery (such as a lithiumbattery), a capacitor wherein a nonaqueous electrolyte is used, or someother article, in a region of the porous body where the diameter ofcells is small, the distance between the active material and theskeleton is small; thus, the electrode can be improved in currentcollecting performance and availability ratio of the active material.Moreover, the region where the cell diameter is small generally has aneffect that in the region, the filled active material drops away lesseasily than in regions where the cell diameter is large. Furthermore,when the aluminum porous body has undergone the step F (compressingstep) in the electrode-producing process illustrated in FIG. 1, in theregion where the cell diameter is small, stronger adhesion is attainedbetween the active material and the skeleton so that the region isimproved in holding performance of the active material.

Therefore, in the case of using, as the base of an electrode, athree-dimensional net-like aluminum porous body of the embodiment [2] asillustrated in FIG. 3, in outer surface regions of the aluminum porousbody, the active material adheres strongly to the skeleton. Thus, theporous body produces an effect of being made better in holdingperformance of the active material. In other words, the active materialis prevented from dropping away so that the battery is improved inlifespan and power characteristic.

For this reason, in the three-dimensional net-like aluminum porous bodyof the present invention, the ratio of the average cell diameter of thecell diameter of the region 1 and that of the region 3 to the celldiameter of the region 2 is preferably 0.9 or less, more preferably 0.7or less. If the ratio of the average cell diameter of the regions 1 and3 to the cell diameter of the region 2 is more than 0.9, it is difficultthat the porous body produces the above-mentioned effect that the porousbody is improved in holding performance of the active material.

As described above, this ratio between the cell diameters is obtained bycounting the number of the skeleton ribs from a microscopic photographof each of the regions as described above, gaining the respectivereciprocals of the resultant numbers, and calculating the ratio betweenthese numerical values. In other words, a calculation is made about theaverage of the reciprocal value of the region 1 and that of the region3, and then this is divided by the reciprocal value of the region 2.

An aluminum porous body wherein the ratio of the average cell diameterof the cell diameter of the region 1 and that of the region 3 to thecell diameter of the region 2 is 0.9 or less as described above may beproduced by use of a polyurethane foam as described in the following inthe aluminum porous body-producing process which will be describedlater. That is, in the step of foaming a polyurethane, at the time offoaming a foaming raw material thereof continuously in a sheet-formmold, the upper and lower planes of the mold are cooled to 5° C. orlower, whereby the growth of cells in the upper and lower planes of thesheet is restrained to give a urethane sheet having a desired celldiameter distribution in the thickness direction thereof. This urethanesheet is plated with aluminum, and the urethane is removed to yield thealuminum porous body, wherein the ratio of the average cell diameter ofthe cell diameter of the region 1 and that of the region 3 to the celldiameter of the region 2 is 0.9 or less.

Similarly to the above-mentioned case, it is effective that aluminumporous bodies different from each other in cell diameter are laminatedonto each other. In other words, the three-dimensional net-like aluminumporous body of the present invention is preferably a three-dimensionalnet-like aluminum porous body wherein three sheet-form aluminum porousbodies D, E and F are laminated in this order onto each other in therespective thickness directions of the porous bodies to be integratedwith each other, and the ratio of the average cell diameter of thealuminum porous bodies D and F to the cell diameter of the aluminumporous body E is 0.9 or less.

In this case, the aluminum porous body E, which is large in celldiameter, is sandwiched between the two aluminum porous bodies D and F,which are small in cell diameter, so that the aluminum porous bodies arelaminated onto each other to be integrated with each other. This mannermakes it possible to produce a three-dimensional net-like aluminumporous body wherein outer surface layer regions (the front surface andthe rear surface) are small in cell diameter, and in reverse an innerregion (the central layer region) is large in cell diameter. Thelamination and integration of the plural aluminum porous bodies makes itpossible to make the three-dimensional net-like aluminum porous bodylarger in thickness than ones in the prior art.

The aluminum porous bodies D to F are selected to set, to 0.9 or less,the ratio of the average cell diameter of the cell diameter of thealuminum porous body D and that of the aluminum porous body F to thecell diameter of the aluminum porous body E, thereby making it possibleto improve the resultant aluminum porous body in holding performance ofan active material therein, and improve the lifespan of the battery. Theratio of the average cell diameter of the aluminum porous bodies D and Fto the cell diameter of the aluminum porous body E is more preferably0.7 or less.

The manner for integrating the laminated aluminum porous bodies D to Fis not particularly limited. For example, the temperature of thelaminated aluminum porous body sheets is raised up to a temperatureclose to the melting point of aluminum in the state that pressure isapplied to the laminated sheets, whereby their skeletons contacting witheach other are melted to be bonded to each other so that the integrationcan be attained. Alternatively, the integration may be attained bybonding surfaces of the laminated aluminum porous bodies to each otherby welding such as spot welding.

Re: Embodiment [3]

In the case of bending a sheet-form aluminum porous body to be workedinto, for example, a cylindrical form, the vicinity of the surfaceregion which is to be the outside of the cylinder is stretched and inreverse a compressing force is applied to the vicinity of the surfaceregion which is to be the inside at the time of the bending.Accordingly, in the case of bending, as an aluminum porous body, analuminum porous body as illustrated in FIG. 4, wherein the cell diameterof a region that is to be the outside when the body is bent is adjustedto be made large and further the cell diameter of a region which is tobe the inside is adjusted to be made small, the bend-working is easilyperformed. Thus, an electrode is improved in windability. In otherwords, usually, by bend-working, skeleton ribs positioned at the outsideof an electrode plate are partially cut with ease. When the ribs arecut, the cut portions break through the separator, so that short circuitis caused. Thus, in the case of bend-working an aluminum porous bodywherein the cell diameter of a region which is to be the outside whenthe body is bent is adjusted to be large, and that of a region which isto be inside is adjusted to be small, the skeleton ribs in the outsideregion having the large cell diameter are not easily cut since theoutside region is large in displacement quantity permitting the skeletonribs to be deformed and finally broken. As a result, the aluminum porousbody is easily bend-worked so that the electrode is improved inwindability.

When a cross section in the thickness direction of the three-dimensionalnet-like aluminum porous body of the present invention is divided intotwo regions of a region 4 and a region 5, the ratio of the cell diameterof the region 4 to that of the region 5 is preferably 1.1 or more, morepreferably 1.5 or more. If the ratio of the cell diameter of the region4 to that of the region 5 is less than 1.1, the above-mentioned effectthat the windability is excellent is not easily obtained.

In order to produce an aluminum porous body wherein the ratio of thecell diameter of the region 4 to that of the region 5 is 1.1 or more asdescribed above, a polyurethane foam as described in the following isused in the aluminum porous body-producing process which will bedescribed later. That is, in the step of foaming a polyurethane, at thetime of foaming a foaming raw material thereof continuously in asheet-form mold, the upper surface of the mold is warmed to 50° C. orhigher, or the lower surface is cooled to 5° C. or lower, whereby thegrowth of cells in the upper surface of the sheet is promoted while thegrowth of cells in the lower surface is restrained to give a urethanesheet having a desired cell diameter distribution in the thicknessdirection thereof. This urethane sheet is plated with aluminum, and theurethane is removed to yield the aluminum porous body, wherein the ratioof the cell diameter of the region 4 to that of the region 5 is 1.1 ormore.

Similarly to the above-mentioned case, it is effective that aluminumporous bodies different from each other in cell diameter are laminatedonto each other. In other words, the three-dimensional net-like aluminumporous body of the present invention is preferably a three-dimensionalnet-like aluminum porous body wherein two sheet-form aluminum porousbodies G and H are laminated in this order onto each other in therespective thickness directions of the porous bodies to be integratedwith each other, and the ratio of the cell diameter of the aluminumporous body G to that of the aluminum porous body H is 1.1 or more.

The aluminum porous body H small in cell diameter and the aluminumporous body G large in cell diameter are laminated onto each other to beintegrated with each other, thereby making it possible to produce athree-dimensional net-like aluminum porous body in which the diameter ofcells in the porous body is uneven in the thickness direction. Moreover,the lamination and integration of the plural aluminum porous bodiesmakes it possible to make the three-dimensional net-like aluminum porousbody larger in thickness than ones in the prior art.

The aluminum porous bodies G and H are selected to set, to 1.1 or more,the ratio of the cell diameter of the aluminum porous body G to that ofthe aluminum porous body H, thereby making it possible to yield analuminum porous body excellent in bending workability. The ratio of thecell diameter of the aluminum porous body G to that of the aluminumporous body H is more preferably 1.5 or more.

The manner for integrating the laminated aluminum porous bodies G and His not particularly limited. For example, the temperature of thelaminated aluminum porous body sheets is raised up to a temperatureclose to the melting point of aluminum in the state that pressure isapplied to the laminated sheets, whereby their skeletons contacting witheach other are melted to be bonded to each other so that the integrationcan be attained. Alternatively, the integration may be attained bybonding surfaces of the laminated aluminum porous bodies to each otherby welding such as spot welding.

The three-dimensional net-like aluminum porous body of the presentinvention has a large-cell-diameter region having a large cell diameterand a small-cell-diameter region having a smaller cell diameter thanthis large cell diameter, as seen in the embodiments [1] to [3]. Forexample, the following are each the large-cell-diameter region: theregions 1 and 3 in the embodiment [1], as well as the outer surfacelayer regions (the regions originating from the aluminum porous bodies Aand C) therein; the region 2 in the embodiment [2], as well as the innerregion (the region originating from the aluminum porous body E) therein;and the region 4 in the embodiment [3], as well as the regionoriginating from the aluminum porous body G therein. Contrarily, forexample, the following are each the small-cell-diameter region: theregion 2 in the embodiment [1], as well as the inner region (the regionoriginating from the aluminum porous body B) therein; the regions 1 and3 in the embodiment [2], as well as the outer surface layer regions (theregions originating from the aluminum porous bodies D and F) therein;and the region 5 in the embodiment [3], as well as the regionoriginating from the aluminum porous body H therein.

When the three-dimensional net-like aluminum porous body of the presentinvention is divided into large-cell-diameter region(s) each having alarge cell diameter and small-cell-diameter region(s) each having asmaller cell diameter than this large cell diameter, the cell diameterof the large-cell-diameter region(s) is preferably 300 μm or more and600 μm or less. This makes it easy that the porous body certainly keeps,for example, active-material-filling performance andorganic-electrolytic-solution-permeability. On the other hand, in thethree-dimensional net-like aluminum porous body of the presentinvention, the cell diameter of the small-cell-diameter region(s) ispreferably 50 μm or more and 300 μm or less. This makes it possible toobtain, for example, an effect of improving the availability ratio ofthe active material. More preferably, the cell diameter of thelarge-cell-diameter region(s) is 300 μm or more and 600 μm or less, andthat of the small-cell-diameter region(s) is 50 μm or more and 300 μm orless. Additionally, the cell diameter of the large-cell-diameterregion(s) is preferably 400 μm or more and 500 μm or less, and that ofthe small-cell-diameter region(s) is preferably 100 μm or more and 200μm or less.

Furthermore, in the three-dimensional net-like aluminum porous body ofthe present invention, the thickness of the small-cell-diameterregion(s) is preferably less than 750 μm. If the small-cell-diameterregion(s) is/are too thick, the active-material-filling performance andthe organic-electrolytic-solution-permeability in thesmall-cell-diameter region(s) may deteriorate. Thus, the thickness ofthe small-cell-diameter region(s) may set to, for example, less than 750μm. The thickness of the whole of the aluminum porous body may be setto, for example, 800 μm or more. The thickness referred to herein is avalue obtained after an active material is filled into the aluminumporous body. Even when this is further subjected to pressure forming,the thickness is a value before the pressure forming.

Hereinafter, a description will be made about a method for producing athree-dimensional net-like aluminum porous body according to the presentinvention. Referring appropriately to the drawings, the following willdescribe, as a typical example, an example wherein an aluminum platingmethod is used as a method for forming an aluminum film on the surfaceof a urethane resin porous body. In the drawings referred tohereinafter, parts or portions to which the same reference number isattached are the same parts or portions, or parts or portionscorresponding thereto. The present invention is not limited to this, andis specified by the claims. The present invention is intended to includeall variations that have meanings equivalent to the meaning of theclaims and are embraced in a scope equivalent to the scope of theclaims.

(Process for Producing Aluminum Structural Body)

FIG. 6 is a flowchart showing a process for producing an aluminumstructural body. Correspondingly to the flowchart, FIGS. 7A to 7D areeach a view that schematically illustrates a situation that an aluminumplating film is formed onto a resin porous body as a core member. Withreference to FIG. 6 and FIGS. 7A to 7D, a description is herein madeabout the progress of the whole of the production process. First, aresin porous body base is prepared [101]. FIG. 7A is an enlargedschematic view of an example of the resin porous body base wherein asurface of the resin porous body having continuous pores is enlarged. Inthe state that the resin porous body, which is a body 1, is used as askeleton, the pores are made. Next, the surface of the resin porous bodyis made electrically conductive [102]. Through this step, a conductivelayer 2 made of a conductor is thinly formed on the surface of the resinporous body 1 as shown in FIG. 7B.

Subsequently, the workpiece is plated with aluminum in a molten salt[103] to form an aluminum plating layer 3 on the surface of theconductive-layer-formed resin porous body (FIG. 7C). In this way, analuminum structural body is yielded wherein the aluminum plating layer 3is formed on the surface of the resin porous body base as a base. Aboutthe resin porous body base, the resin porous body base is removed [104].

The resin foam porous body 1 is removed by decomposition or the like, sothat the aluminum structural body (porous body) in which only the metallayer remains can be yielded (FIG. 7D). Hereinafter, each of the stepswill be described in turn.

(Preparation of Porous Resin Shaped Body)

Prepared is a porous resin shaped body having a three-dimensionalnet-like structure and having continuous pores. About the raw materialof the porous resin shaped body, any resin may be selected. An exampleof the raw material is a resin foam shaped body of polyurethane,melamine, polypropylene, or polyethylene. Herein, the wording “resinfoam shaped body” is used; however, a resin shaped body having any shapemay be selected as far as the body has pores continued to each other(continuous pores). Instead of the resin foam shaped body, for example,a body obtained by entangling resin fibers with each other into a formlike a nonwoven fabric may be used. The porosity and the pore diameter(cell diameter) of the resin foam shaped body are preferably set intothe range of 80 to 98% and that of 50 to 500 μm, respectively. Each ofurethane foam and melamine foam can be preferably used for the resinfoam shaped body since these foams have a high porosity, porecontinuity, and excellent thermal decomposability.

Urethane foam is preferred because of uniformity of pores therein, highavailability, and others. Melamine foam is preferred since the foamgives a shaped body small in pore diameter.

In many cases, the porous resin shaped body contains residues of afoaming agent, an unreacted monomer, and others in the step of producingthe foamed body; thus, it is preferred for subsequent steps to subjectthe shaped body to a washing treatment. FIG. 8 shows, as an example ofthe porous resin shaped body, a urethane foam subjected to a washingtreatment as a pre-treatment. The resin shaped body functions as askeleton to constitute a three-dimensional net, whereby pores continuedto each other in the whole are made. Ribs of the skeleton of theurethane foam are made into a substantially triangular form in any crosssection perpendicular to the direction in which the ribs are extended.The porosity is defined by the following equation:Porosity=(1−(the mass [g] of the porous material)/(the volume [cm³] ofthe porous material×the density of the raw material)×100

The pore diameter (cell diameter) is obtained by enlarging the surfaceof the resin shaped body through a microscopic photograph, counting thenumber of pores therein per inch (25.4 mm), as the number of cells, andthen calculating a mean value as a value from the following: the averagepore diameter=25.4 mm/the number of the cells.

(Surface of Resin Porous Body Made Electrically Conductive)

In order to electroplate the workpiece, the surface of the resin foam isbeforehand subjected to an electrically conduction treatment. Thetreatment is not particularly limited as far as it is a treatmentcapable of forming a layer having electroconductivity onto the surfaceof the resin porous body. Any method may be selected, examples of whichinclude electroless plating with a conductive metal such as nickel,vapor deposition and sputtering of aluminum or some other, and coatingwith a conductive paint containing conductive particles of carbon orsome other.

(Formation of Aluminum Layer onto Surface of Resin Porous Body)

Examples of a method for forming an aluminum layer onto the surface ofthe resin porous body include (i) vapor deposition methods (such as avacuum vapor deposition, a sputtering method, and a laser ablationmethod), (ii) a plating method, and (iii) a paste painting method. It ispreferred to use, out of these methods, a molten salt plating method asa method suitable for mass production. Hereinafter, the molten saltplating method will be described in detail.

-Molten Salt Plating-

Electroplating is conducted in a molten salt to form an aluminum platinglayer on the surface of the resin porous body.

When plating with aluminum is conducted in a molten salt bath, auniformly thick aluminum layer can be formed on the surface of acomplicated skeleton structure, in particular, that of a resin porousbody having a three-dimensional net-like structure.

The resin porous body, the surface of which has been made electricallyconductive, is used as a negative electrode, and an aluminum piece isused as a positive electrode. In this state, a direct current is appliedinto the molten salt.

The molten salt may be an organic molten salt that is a eutectic saltcomposed of an organic halide and an aluminum halide or an inorganicmolten salt that is a eutectic salt composed of a halide of an alkalimetal and an aluminum halide. It is preferred to use an organic moltensalt bath that is molten at a relatively low temperature since the resinporous body as a base can be plated without being decomposed. Theorganic halide may be an imidazolium salt, a pyridinium salt or someother. Specifically, the halide is preferably1-ethyl-3-methylimidazolium chloride (EMIC), or butylpyridinium chloride(BPC).

When water or oxygen is incorporated into the molten salt, the moltensalt is deteriorated. It is therefore preferred to conduct the platingunder the atmosphere of an inert gas such as nitrogen or argon in aclosed environment.

The molten salt bath is preferably a molten salt bath containingnitrogen, in particular, an imidazolium salt bath. When a salt that ismolten at high temperature is used as a molten salt, the dissolution ordecomposition of the resin into the molten salt becomes speedier thanthe growth of a plating layer, so that no plating layer can be formed onthe resin porous body surface. The imidazolium salt bath can be usedwithout affecting the resin even at a relatively low temperature. Theimidazolium salt is preferably a salt containing an imidazolium cationhaving alkyl groups at the 1 and 3 positions thereof, and is mostpreferably an aluminum chloride-1-ethyl-3-methylimidazolium chloride(AlCl₃-EMIC) type molten salt since the salt is high in stability and isnot easily decomposed. The temperature of the molten salt bath is 10 to100° C., preferably 25 to 45° C. since a urethane resin foam, a melamineresin foam or some other can be plated. As the temperature is lower, therange of current densities making plating possible is narrower so thatthe whole of the porous body surface is less easily plated. At a hightemperature over 100° C., there is easily generated an inconveniencethat the shape of the resin base is damaged.

It is reported to add, to AlCl₃-EMIC, an additive such as xylene,benzene, toluene, or 1,10-phenanthroline. The inventors have found outthat the addition of 1,10-phenanthroline can give an effect especial forthe formation of an aluminum porous body, in particular, when platingwith aluminum is applied to a resin porous body having athree-dimensional net-like structure. In other words, the addition givesa first characteristic that the aluminum skeleton that forms the porousbody is not easily broken, and a second characteristic that the porousbody can be evenly plated to give a small difference in thicknessbetween the plating on the surface region of the porous body and that onthe inside thereof.

In a case where the aluminum porous body is pressed when finished, or insome other case, the two characteristics of the high breaking resistanceand the uniformity of the plating thickness on the outside and theinside make it possible to yield a pressed porous body where the wholeof the skeleton is not easily broken and the pressing has been evenlyattained. When any aluminum porous body is used as an electrode materialfor a battery or some other, an electrode active material is filled intothe electrode and then the electrode is pressed to make the densitythereof high; in the step of filling the active material or pressing theelectrode, the skeleton is easily broken. Thus, for such a usage, theporous body of the present invention is very useful.

From the above-mentioned matters, it is preferred to add an organicsolvent to the molten salt bath. 1,10-Phenanthroline is in particularpreferably used. The amount thereof to be added to the plating bath ispreferably 0.25 to 7 g/L. If the amount is 0.25 g/L or less, a platinglayer brittle and poor in flatness and smoothness is obtained andfurther the effect of decreasing the difference between the thickness onthe surface layer and that on the inside is not easily obtained. If theamount is 7 g/L or more, the plating efficiency is declined so that apredetermined plating thickness is not easily obtained.

FIG. 9 is a view that schematically illustrates the structure of anapparatus for plating band-form resin continuously with aluminum.Illustrated is a mechanics for feeding a band-form resin 22, having thesurface made electrically conductive, from the left in this drawing tothe right. A first plating tank 21 a is composed of a cylindricalelectrode 24, a positive electrode 25 set to an inner wall of acontainer and made of aluminum, and a plating bath 23. The band-formresin 22 is passed in the plating bath 23 along the cylindricalelectrode 24, whereby electric current easily flows evenly into thewhole of the resin porous body so that even plating can be obtained.Plating tanks 21 b are tanks for depositing plating layers thickly andevenly, and are formed to repeat plating in the plural tanks. While theband-form resin 22, the surface of which has been made electricallyconductive, is successively fed by means of feeding rollers andelectrode rollers 26 functioning also as out-of-tank electricity-sendingnegative electrodes, the resin 22 is passed through plating baths 28 toplate the resin. In the tanks, positive electrodes 27 made of aluminumare fitted to both surfaces of the resin porous body to interpose theplating baths 28 between the porous body and both of the surfaces, sothat evener plating layers can be deposited onto both the surfaces ofthe resin porous body, respectively. Nitrogen is blown onto the platedaluminum porous body to remove the plating liquid sufficiently. Theworkpiece is then washed with water to yield an aluminum porous body.

In the meantime, an inorganic salt bath may be used for a molten salt asfar as the resin is neither dissolved nor damaged in any other manner.The inorganic salt bath is typically a two-component type ormulti-component type salt of AlCl₃—XCl wherein X is an alkali metal.Such an inorganic salt bath is generally higher in melting temperaturethan organic salt baths such as an imidazolium salt bath; however, theinorganic salt bath is less restricted by environment factors such aswater and oxygen, so that the salt can be put into practical use at lowcosts as a whole. When the resin is a foamed melamine resin, the resincan be used at a higher temperature than any foamed urethane resin.Thus, an inorganic salt bath of 60 to 150° C. temperature is used.

The other methods, i.e., the vapor deposition methods (i) and the pastepainting method (iii) will be described.

-Gas Phase Methods-

In a vacuum vapor deposition, for example, an electron beam is radiatedonto aluminum as a raw material to melt and vaporize aluminum to depositthe aluminum onto the surface of the resin porous body, whereby analuminum layer can be formed. In a sputtering method, for example,plasma is radiated onto an aluminum target to gasify the aluminum so asto be deposited onto the surface of the resin porous body, whereby analuminum layer can be formed. In a laser ablation method, for example,aluminum is molten and vaporized by irradiation with a laser to depositaluminum onto the surface of the resin porous body, whereby an aluminumlayer can be formed.

-Paste Painting Method-

In the paste painting method, use is made of, for example, an aluminumpaste wherein an aluminum powder, a binder, and an organic solvent aremixed with each other. The aluminum paste is painted onto the resinporous body surface, and then heated to remove the binder and theorganic solvent and further sinter the aluminum paste. The sintering maybe performed once, or may be dividedly performed plural times. Forexample, by painting the aluminum paste, heating the resin body at lowtemperature to remove the organic solvent, and then heating the resinporous body in the state of being immersed in a molten salt, the resincan be thermally decomposed and simultaneously the aluminum paste can besintered. The sintering is preferably performed in a non-oxidizingatmosphere.

Through the above-mentioned steps, obtained is an aluminum structuralbody having the resin shaped body as the core of its skeleton (aluminumporous body). Depending on the use thereof for a filter that may be ofvarious types, a catalyst carrier, or some other, this resultantaluminum porous body may be used, as it is, as a complex of the resinand the metal. When the resultant is used as a metallic structural bodycontaining no resin in light of a restriction of the environment for theuse, the resin may be removed. The removal of the resin may be attainedby any method, such as decomposition (dissolution) by use of an organicsolvent, a molten salt, or supercritical water, or heatingdecomposition. Although heating decomposition at high temperature, andthe like are simple and easy, the oxidization of aluminum is followedthereby. Once aluminum is oxidized, the metal is not easily reduced,this situation being different from that of nickel or the like. Thus,when aluminum is used as, for example, a material for an electrode of abattery or some other member, aluminum is oxidized to loseelectroconductivity. Thus, the metal cannot be used.

Therefore, in order not to oxidize aluminum, it is preferred to use amethod of removing the resin by thermal decomposition in a molten saltthat will be described below.

(Removal of the Resin: Thermal Decomposition in Molten Salt)

The thermal decomposition in a molten salt is performed by a methoddescribed below. The resin shaped body the surface of which has thealuminum plating layer formed is immersed in a molten salt. While anegative potential is applied to the aluminum layer, the resin foamshaped body is heated to be decomposed. The application of the negativepotential in the state that the body is immersed in the molten saltmakes it possible to decompose the resin foam shaped body withoutoxidizing the aluminum. The temperature for the heating may beappropriately selected in accordance with the kind of the resin foamshaped body; however, in order not to melt the aluminum, it is necessaryto treat the body at the melting point (660° C.) of aluminum, or lower.The temperature is preferably 500° C. or higher and 600° C. or lower.The quantity of the applied negative potential is made into a minus siderelative to the reduction potential of aluminum and a plus side relativeto the reduction potential of the cation in the molten salt.

The molten salt used for the thermal decomposition of the resin may be ahalide salt of an alkali metal or alkaline earth metal which makes theelectrode potential of the aluminum lower. Specifically, the saltpreferably contains at least one selected from the group consisting oflithium chloride (LiCl), potassium chloride (KCl), sodium chloride(NaCl), and aluminum chloride (AlCl₃). Such a method makes it possibleto yield an aluminum porous body having continuous pores and having, onthe surface thereof, a thin oxide layer so as to be small in oxygencontent. Specifically, the oxygen content in the aluminum porous bodysurface is 3.1% by mass or less. An active material contacts the surfaceof the aluminum porous body functioning as a current collector so thatelectrons are donated and received between the porous body and theactive material when the battery is charged and discharged; therefore,the nature of the porous body surface affects characteristics of thebattery. In the aluminum porous body surface, the oxygen content is 3.1%by mass or less, whereby the oxygen content in the surface is smallerthan in aluminum porous bodies in the prior art, so that the electricalresistance of the porous body surface is lower. Thus, this porous bodycan be expected to improve battery characteristics (in particular,high-rate discharge characteristic). The oxygen content referred toherein is a value obtained by analyzing the aluminum porous body surfacequantitatively by EDX (energy dispersive X-ray analysis) at anaccelerating voltage of 15 kV. The wording that the oxygen content is3.1% by mass or less denotes the detection limit according to EDX, orless. A specific description of an analyzing instrument therefor will bemade later. Additionally, the aluminum porous body wherein the oxygencontent in the surface is 3.1% by mass or less is less easily crackedand more easily deformed when an active material is filled into theporous body and then the resultant is subjected to pressure forming thanin conventional aluminum porous bodies having a larger oxygen content intheir surface. For this reason, the pressure forming makes it possibleto improve electrode density (the filling density of the activematerial) and improve the adhesiveness between the porous body and theactive material while the current collecting performance of the porousbody is kept.

The following will describe a process for producing an electrode fromthe aluminum porous body yielded as described above.

FIG. 1 is a view referred to in order to describe an example of aprocess for producing an electrode continuously from the aluminum porousbody.

(Thickness Adjusting Step)

From a raw material roll wherein a sheet of the aluminum porous body iswound, the aluminum porous body sheet is wound back, and the thicknessis adjusted into an optimal thickness and further surfaces thereof aremade flat and smooth by means of a press machine in a thicknessadjusting step. The final thickness of the aluminum porous body isappropriately decided in accordance with the usage of the electrodeobtained therefrom. This thickness adjusting step is a compressing stepbefore the porous body is made into the final thickness; thus, theporous body is compressed to such a degree that the body is to have athickness permitting a processing in the next step to be easilyattained. The press machine may be a flat press or a roller press. Theflat press is preferred for restraining the current collector from beingelongated; however, the press is unsuitable for mass production. Thus,it is preferred to use the roller press, which is capable of attaining acontinuous processing.

(Lead Welding Step)

-Compression of End of Aluminum Porous Body-

When the aluminum porous body is used as an electrode current collectorof a secondary battery or some other, it is necessary to melt a tab leadfor leading-out to the outside, and bond the tab lead onto the aluminumporous body. In the case of an electrode wherein the aluminum porousbody is used, the electrode has no strong metallic region. Thus, no leadpiece can be directly welded thereto. For this reason, an end of thealuminum porous body is compressed to make the end into a foil pieceform. In this manner, mechanical strength is given thereto, and then thetab lead is welded thereto.

A description is made about an example of a method for working the endof the aluminum porous body.

FIG. 10 is a view that schematically illustrates the compressing step.

A tool for the compression may be a rotatable roller.

The compressed region is made into a thickness of 0.05 mm or more and0.2 mm or less (for example, about 0.1 mm), whereby the end can gain apredetermined mechanical strength.

In FIG. 11, the center of the aluminum porous body, which is an aluminumporous body 34 having a width corresponding to that of two sheets, iscompressed by means of a rotatable roller 35 as the compressing tool toform a compressed region 33. After the compression, the center of thecompressed region 33 is cut to yield two electrode current collectorseach having, at an end thereof, the compressed region.

A plurality of rotatable rollers may be used to form a plurality ofband-form compressed regions in the center of the aluminum porous body,and then each of the band-form compressed regions is cut along thecentral line thereof, whereby a plurality of current collectors can beyielded.

-Bonding of Tab Lead onto Edge of Electrode-

The tab lead is bonded to the compressed region of the end of thecurrent collector, which has been obtained as described above. It ispreferred that the tab lead is a metal foil for decreasing theelectrical resistance of the electrode, and the metal foil is bonded toat least one side surface of the edge of the electrode. In order todecrease the electrical resistance, it is preferred to use, as a methodfor the bonding, welding. If the width of the area onto which the metalfoil is to be welded is too large, a useless space is increased in thebattery so that the capacity density of the battery is lowered. Thus,the width is preferably 10 mm or less. If the width is too small, thewelding becomes difficult and further the power collecting effect isalso declined. Thus, the width is preferably 1 mm or more.

The method for the welding may be resistance welding, ultrasonic weldingor some other method. Ultrasonic welding is preferred since the methodcan give a wide bonding area.

-Metal Foil-

The material of the metal foil is preferably aluminum, consideringelectrical resistance and resistance against electrolytes. If thematerial contains impurities, the impurities elute out or react in thebattery and the capacitor; thus, it is preferred to use an aluminum foilhaving a purity of 99.99% or more. It is also preferred that thethickness of the welded region is smaller than that of the electrodeitself.

The thickness of the aluminum foil is preferably 20 to 500 μm.

The metal foil may be welded before or after an active material isfilled into the current collector. When the welding is performed beforethe filling, the active material is favorably restrained from droppingaway. In the case of, in particular, ultrasonic welding, it is preferredto perform the welding before the filling. The active material mayadhere onto the welded region. However, the paste may be peeled in themiddle of the step; thus, it is preferred to mask it in such a mannerthat the paste cannot be filled thereinto.

The above has described the end-compressing step, and thetab-lead-bonding step as different steps. However, the compressing stepand the bonding step may be simultaneously performed. In this case, theused compressing roller may be a roller wherein a roller regioncontacting the tab-lead-bonding-end of the aluminum porous body sheetcan attain resistance welding. The aluminum porous body sheet and themetal foil are simultaneously supplied to this roller, thereby making itpossible to perform the compression of the end and the welding of themetal foil onto the compressed region simultaneously.

(Step of Filling Active Material)

An active material is filled into the current collector yielded asdescribed above to yield an electrode. The active material isappropriately selected in accordance with a use object of the electrode.

For the filling of the active material, a known method, such as animmersion filling method or a coating method, may be used. Examples ofthe coating method include a roll coating method, an applicator coatingmethod, an electrostatic coating method, a powder coating method, aspray coating method, a spray coater coating method, a bar coatercoating method, a roll coater coating method, a dip coater coatingmethod, a doctor blade coating method, a wire bar coating method, aknife coater coating method, and a blade coating method, and screenprinting methods.

At the time of filling the active material, a conduction aid and abinder may be added thereto if necessary. Thereinto is incorporated anorganic solvent to prepare a slurry, and this slurry is filled into thealuminum porous body by the above-mentioned filling method.

In FIG. 12 is shown a method for filling the slurry into the porous bodyby a roll coating method. As shown in this drawing, the slurry issupplied onto the porous body sheet, and this is passed through a pairof rotatable rollers that are opposed to each other to have apredetermined gap therebetween. When the sheet is passed through therotatable rollers, the slurry is pressed and filled into the porousbody.

(Drying Step)

The porous body filled with the active material is fed into a dryingmachine, and heated to evaporate and remove the organic solvent, therebyyielding an electrode material wherein the active material is fixed inthe porous body.

(Compressing Step)

The electrode material is dried, and then compressed into a finalthickness in a compressing step. The press machine used therefor may bea flat press or a roller press. The flat press is preferred forrestraining the current collector from being elongated; however, thispress is unsuitable for mass production. Thus, it is preferred to usethe roller press, which is capable of attaining a continuous processing.

In a compressing step F in FIG. 1, a case where the electrode materialis compressed by a roller press is shown.

(Cutting Step)

In order to improve the mass productivity of electrode material, it ispreferred to make the width of the sheet of the aluminum porous bodyequal to the total width of two or more out of final sheet-products, andcut this porous body sheet along the advancing direction of the sheetwith a plurality of blades, thereby preparing a plurality of long sheetsof the electrode material. This cutting step is a step of dividing thelong electrode material into plural long sheets of the electrodematerial.

(Winding-up Step)

This step is a step of winding up the electrode material in the form ofthe long sheets yielded in the cutting step onto a winding-up roller.

The following will describe the usage of the electrode material yieldedas described above.

Main examples of an article wherein the electrode material, in which thealuminum porous body is used as a current collector, is used include anelectrode for a nonaqueous electrolyte battery, such as a lithiumbattery or a molten salt battery; and an electrode, for a capacitor,wherein a nonaqueous electrolyte is used.

Hereinafter, use of these articles will be described.

(Lithium Battery)

The following will describe an electrode material for a battery, and abattery in each of which the aluminum porous body is used. When thealuminum porous body is used for a positive electrode of a lithiumbattery, the following may be used as an active material therefor:lithium cobaltate (LiCoO₂), lithium manganate (LiMn₂O₄), lithiumnickelate (LiNiO₂) or some other. The active material is used incombination with a conduction aid and a binder. About any conventionalpositive electrode material for a lithium battery, an active material isapplied onto surfaces of its aluminum foil. In order to improve batterycapacity per unit area, the paint thickness of the active material ismade large. Moreover, in order to make good use of the active material,it is necessary that the aluminum foil electrically contacts the activematerial; therefore, the active material is used in the form of amixture with a conduction aid. By contrast, the aluminum porous body ofthe present invention is high in porosity and large in surface area perunit area. Thus, even when an active material is thinly carried onto thesurface of the porous body, good use can be made of the active materialso that the capacity of the battery can be improved and further theblend amount of the conduction aid can be made small. In a lithiumbattery, for its positive electrode, the above-mentioned positiveelectrode material is used while for its negative electrode, graphite,lithium titanate (Li₄Ti₅O₁₂), an alloy of Si and others, metalliclithium, or some other is used. For its electrolyte, an organicelectrolyte or a solid electrolyte is used. Such a lithium battery canbe improved in capacity even when the electrode area thereof is small.Thus, the battery can be made high in energy density than lithiumbatteries in the prior art.

(Electrode for Lithium Battery)

The electrolyte used in lithium batteries are classified into anonaqueous electrolyte and a solid electrolyte.

FIG. 13 is a vertical sectional view of an all-solid-state lithiumbattery. This all-solid-state lithium battery, which is a battery 60,has a positive electrode 61, a negative electrode 62, and an electrolytelayer 63 arranged between the two electrodes.

In the case of an organic solvent-based lithium battery, a separatormade of a porous resin, a paper piece, or some other is arranged at aposition corresponding to the electrolyte layer 63 between the positiveelectrode 61 and the negative electrode 62, and a nonaqueous electrolytecontaining an organic liquid as a solvent and a lithium salt as a soluteis held in pores in the positive electrode, the negative electrode andthe separators. In this case, the separator wherein the nonaqueouselectrolyte is held corresponds to the electrolyte layer 63. In the caseof the all-solid-state lithium battery, a solid electrolyte such asLi₂S—P₂S₆ is used. The positive electrode 61 is composed of a positiveelectrode layer (positive electrode body) 64 and a current collector ofpositive electrode 65. The negative electrode 62 is composed of anegative electrode layer 66 and a negative electrode current collector67.

(Active Material to be Filled into Aluminum Porous Body)

When the aluminum porous body is used for a positive electrode of alithium battery, a material capable of inserting and removing lithiumcan be used as an active material therefor. This material is filled intothe aluminum porous body, thereby making it possible to yield anelectrode suitable for a lithium secondary battery. Examples of thematerial of the positive electrode active material include lithiumcobaltate (LiCoO₂), lithium nickelate (LiNiO₂), lithium nickel cobaltoxide (LiCo_(0.3)Ni_(0.7)O₂), lithium manganate (LiMn₂O₄), lithiumtitanate (Li₄Ti₅O₁₂), lithium manganate compounds (LiM_(y)Mn_(2-y)O₄wherein M=Cr, Co or Ni), olivine compounds, which are lithium ironphosphate and compounds thereof (LiFePO₄, and LiFe_(0.5)Mn_(0.5)PO₄),and other transition metal oxides. The transition metal element(s)contained in each of these materials may be partially substituted withanother transition metal oxide. The active material is used incombination with a conduction aid and a binder.

Other examples of the positive electrode active material include sulfidetype chalcogen compounds such as TiS₂, V₂S₃, FeS, FeS₂, and LiMSxwherein M is a transition metal element such as Mo, Ti, Cu, Ni or Fe, orSb, Sn or Pb), and lithium metals each having a skeleton of a metaloxide such as TiO₂, Cr₃O₈, V₂O₅, or MnO₂. Lithium titanate (Li₄Ti₅O₁₂),which has been described above, may be used as a negative electrodeactive material.

(Electrolytic Solution Used in Lithium Battery)

The nonaqueous electrolyte is used in a polar aprotic organic solvent,and specific examples of the solvent include ethylene carbonate, diethylcarbonate, dimethyl carbonate, propylene carbonate, γ-butyrolactone, andsulfolane. As a supporting salt therein, the following may be used:lithium tetrafluoroborate, lithium hexafluorophosphate, an imide salt,or some other.

(Solid Electrolyte Filled into Aluminum Porous Body)

Besides the active material, a solid electrolyte may be further addedand filled into the porous body. The filling of the active material andthe solid electrolyte into the aluminum porous body makes it possible torender the aluminum porous body an electrode suitable for anall-solid-state lithium battery. However, the proportion of the activematerial in the substances filled into the aluminum porous body is setpreferably into 50% by mass or more, more preferably into 70% by mass ormore in order to keep the discharge capacity certainly.

The solid electrolyte is preferably a sulfide type solid electrolyte,which is high in lithium ion conductivity. An example of this sulfidetype solid electrolyte is a sulfide type solid electrolyte containinglithium, phosphorus, and sulfur. The sulfide type solid electrolyte mayfurther contain 0, Al, B, Si, Ge or some other element.

The sulfide type solid electrolyte may be obtained by a known method.The method is, for example, a method of preparing lithium sulfide (Li₂S)and diphosphorus pentasulfide (P₂S₅) as starting materials, mixing Li₂Sand P₂S₅ with each other at a mole ratio of about 50:50 to 80:20,melting this mixture, and then cooling the mixture rapidly (the meltingand rapid quenching method), and a method of milling this mixturemechanically (the mechanical milling method).

The sulfide type solid electrolyte obtained by this method is amorphous.The amorphous electrolyte may be used as it is. By subjecting thiselectrolyte to a heating treatment, the electrolyte may be used in theform of a crystalline sulfide type solid electrolyte. By thecrystallization, the solid electrolyte can be expected to be improved inlithium ion conductivity.

(Filling Active Material into Aluminum Porous Body)

For the filling of the active material (the active material and thesolid electrolyte), a known method, such as an immersion filling methodor a coating method, may be used. Examples of the coating method includea roll coating method, an applicator coating method, an electrostaticcoating method, a powder coating method, a spray coating method, a spraycoater coating method, a bar coater coating method, a roll coatercoating method, a dip coater coating method, a doctor blade coatingmethod, a wire bar coating method, a knife coater coating method, and ablade coating method, and screen printing methods.

At the time of the filling of the active material (the active materialand the solid electrolyte), for example, a conduction aid and a binderare optionally added thereto, and then an organic solvent isincorporated into this mixture to prepare a slurry mixture of positiveelectrode materials. This is filled into the aluminum porous body by theabove-mentioned method. In order to prevent the aluminum porous bodyfrom being oxidized, it is preferred to perform the filling of theactive material (the active material and the solid electrolyte) in aninert gas atmosphere. The conduction aid may be, for example, a carbonblack such as acetylene black (AB) or Ketjen Black (KB). The binder maybe, for example, polyvinylidene fluoride (PVDF) orpolytetrafluoroethylene (PTFE).

The organic solvent used when the slurry mixture of positive electrodematerials is prepared may be appropriately selected as far as thesolvent produces no bad effect onto the materials filled into thealuminum porous body (i.e., the active material, the conduction aid, thebinder and the optional solid electrolyte). Examples of the organicsolvent include n-hexane, cyclohexane, heptane, toluene, xylene,trimethylbenzene, dimethyl carbonate, diethyl carbonate, ethylmethylcarbonate, propylene carbonate, ethylene carbonate, butylene carbonate,vinylene carbonate, vinylethylene carbonate, tetrahydrofuran,1,4-dioxane, 1,3-dioxolane, ethylene glycol, and N-ethyl-2-pyrrolidone.

About conventional positive electrode materials for a lithium battery,an active material is painted onto their aluminum foil surfaces. Thepaint thickness of the active material is made large in order to improvebattery capacity per unit area. In order to make good use of the activematerial, it is necessary that the aluminum foil electrically contactsthe active material; thus, the active material is used in the form of amixture with a conduction aid. By contrast, the aluminum porous body ishigh in porosity and large in surface area per unit area thereof. Thus,even when the active material is thinly carried on the porous bodysurface, good use can be made of the active material so that thecapacity of the battery can be improved and further the blend amount ofthe conduction aid can be reduced. In a lithium battery, theabove-mentioned positive electrode material, graphite, and an organicelectrolyte are used as its positive electrode, its negative electrode,and its electrolyte, respectively. Even when this lithium battery issmall in electrode area, the battery can be improved in capacity so thatthe battery can be made higher in energy density than conventionallithium batteries.

(Electrode for Capacitor Wherein Nonaqueous Electrolytic Solution isUsed)

FIG. 14 is a schematic sectional view illustrating an example of acapacitor making use of a nonaqueous electrolyte, wherein an electrodematerial for a capacitor making use of the nonaqueous electrolyte isused. In an organic electrolyte 143 partitioned by a separator 142,electrode materials in each of which an electrode active material iscarried on an aluminum porous body are arranged as polarizableelectrodes 141. The polarizable electrodes 141 are each connected to alead wire 144. The whole of these members is held in a case 145. The useof the aluminum porous body as each current collector makes the surfacearea of the current collector large. Thus, even when activated carbon asthe active material is thinly painted, the obtained capacitor, whereinthe nonaqueous electrolyte is used, makes it possible to attain a highpower and a high capacity.

In order to produce this electrode for a capacitor making use of thenonaqueous electrolyte, activated carbon is used, in the currentcollectors, as the respective active materials. The activated carbon isused in combination with a conduction aid and a binder. The conductionaid may be, for example, graphite, or carbon nanotubes. The binder maybe, for example, polytetrafluoroethylene (PTFE), or a styrene/butadienerubber.

A paste of the activated carbon is filled. In order to make the capacityof the capacitor large, it is more preferred that the amount of theactivated carbon as a main component is larger. After the paste is dried(after the solvent is removed), the proportion of the activated carbonin the composition is preferably 90% or more. Although the conductionaid and the binder are necessary, the respective proportions thereof arepreferably as small as possible since these components cause a fall inthe capacity and the binder further causes an increase in the internalresistance. Preferably, the proportion of the conduction aid is 10% bymass or less, and that of the binder is 10% by mass or less.

As the surface area of the activated carbon is larger, the capacity ofthe capacitor is larger. Thus, the specific surface area is preferably2000 m²/g or more. The conduction aid may be Ketjen Black, acetyleneblack or a carbon fiber, or a composite material thereof. The binder maybe polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol,carboxymethylcellulose, xanthan gum, or some other. It is advisable toselect, as the solvent, water or an organic solvent appropriately inaccordance with the kind of the binder. As the organic solvent,N-methyl-2-pyrrolidone is used in many cases. When water is used as thesolvent, a surfactant may be used to improve the paste in fillingperformance.

The components of the above-mentioned electrode material, which is mademainly of activated carbon, are mixed with each other, and stirred,thereby obtaining an activated carbon paste. This activated carbon pasteis filled into the current collector, and dried, and optionally thethickness of the resultant is adjusted by a roller press or some othermachine, thereby yielding an electrode for a capacitor.

(Production of Capacitor)

The electrode yielded as described above is punched out into electrodepieces having an appropriate size, and two of the pieces are prepared.The two are opposed to each other to sandwich a separator therebetween.While necessary spacers are used, the combined members are packaged intoa cell case. The members are then impregnated with an electrolyte.Finally, a lid is fitted to the case to interpose an insulating gaskettherebetween to seal the inside, thereby making it possible to produce acapacitor wherein the nonaqueous electrolyte is used. When thenonaqueous material is used, the content of water in the capacitor ismade limitlessly small. For this matter, the production of the capacitoris made in an environment wherein the water content is small, and thesealing is attained in a reduced-pressure environment. As far as thecurrent collector or the electrode of the present invention is used in acapacitor, the capacitor is not particularly limited in productionprocess. Thus, the capacitor may be a capacitor that is produced by anyproduction process other than the above-mentioned process.

The negative electrode is not particularly limited, and may be anyconventional electrode as a negative electrode. However, a conventionalelectrode wherein an aluminum foil is used as a current collector issmall in capacity; thus, the negative electrode is preferably anelectrode wherein an active material is filled into a porous body, suchas the above-mentioned foamed nickel.

The electrolyte may be a solution of an aqueous type or a nonaqueoustype. The nonaqueous electrolyte is preferred since the solution makesit possible to set a high voltage. In the aqueous type electrolyte,potassium hydroxide or some other may be used as its electrolyte. In thenonaqueous type electrolyte, an ionic liquid may be used, examplesthereof including many combinations each composed of a cation and ananion. The cation may be, for example, a lower aliphatic quaternaryammonium, a lower aliphatic quaternary phosphonium, or an imidazoliumsalt, and the anion may be, for example, a metal chloride ion, a metalfluoride ion, or an imide compound such as bis(fluorosulfonyl)imide. Apolar aprotic organic solvent may be used, specific examples thereofincluding ethylene carbonate, diethyl carbonate, dimethyl carbonate,propylene carbonate, γ-butyrolactone, and sulfolane. A supporting saltin the nonaqueous electrolyte may be lithium tetrafluoroborate, lithiumhexafluorophosphate, an imide salt, or some other.

(Electrode for Molten Salt Battery)

The aluminum porous body may be used as an electrode material for amolten salt battery. When the aluminum porous body is used as a positiveelectrode material thereof, the following may be used as an activematerial therefor: sodium chromite (NaCrO₂), titanium disulfide (TiS₂),or any other metal compound capable of intercalating the cation of themolten salt, which is an electrolyte. The active material is used incombination with a conduction aid and a binder. The conduction aid maybe acetylene black, or some other. The binder may bepolytetrafluoroethylene (PTFE), or some other. When sodium chromate isused as the active material and acetylene black is used as theconduction aid, PTFE is preferred since this polymer makes it possibleto bond and fix the two more strongly.

The aluminum porous body may be used as a negative electrode activematerial for a molten salt battery. When the aluminum porous body isused as the negative electrode active material, the following may beused as an active material therefor: a simple substance of sodium, analloy of sodium and another metal, carbon, or some other. Sodium has amelting point of about 98° C., and further the metal is softened as thetemperature thereof is raised; therefore, it is preferred that sodium iscombined with another metal or a nonmetal (such as Si, Sn or In) to bealloyed. A substance obtained by alloying sodium and Sn is particularlypreferred since the substance is easily handled. Sodium or any sodiumalloy can be carried onto the surface of the aluminum porous body byelectroplating, hot dipping, or some other method. By depositing sodium,and a metal or nonmetal (such as Si) to be alloyed therewith onto thealuminum porous body by plating or some other method, and thenperforming electrification in a molten salt battery, a sodium alloy canalso be prepared.

FIG. 15 is a schematic sectional view illustrating an example of amolten salt battery wherein the above-mentioned battery electrodematerial is used. The molten salt battery is a battery obtained bypackaging, into a case 127, a positive electrode 121 in which a positiveelectrode active material is carried on the surface of aluminum skeletonregions of an aluminum porous body, a negative electrode 122 in which anegative electrode active material is carried on the surface of aluminumskeleton regions of another aluminum porous body, and a separator 123impregnated with a molten salt which is an electrolyte. Between the topsurface of the case 127 and the negative electrode, a pressing member126 is arranged which is composed of a holding plate 124 and a spring125 for pressing the holding plate. The setting of the pressing membermakes it possible to press the positive electrode 121, the negativeelectrode 122 and the separator 123 evenly to contact the members eachother even when these members are changed in volume. The currentcollector (aluminum porous body) of the positive electrode 121 and thecurrent collector (aluminum porous body) of the negative electrode 122are connected to a positive electrode terminal 128 and a negativeelectrode terminal 129, respectively, through respective lead wires 130.

The molten salt as the electrolyte may be an inorganic salt or organicsalt which is molten at the operating temperature, and which may be ofvarious types. The cation of the molten salt may be one or more selectedfrom alkali metals such as lithium (Li), sodium (Na), potassium (K),rubidium (Rb), and cesium (Cs), and alkaline earth metals such asberyllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium(Ba).

In order to lower the melting point of the molten salt, it is preferredto use two or more salts in a mixture form. For example, the use of thefollowing combination makes it possible to make the operatingtemperature of the battery to 90° C. or lower: potassiumbis(fluorosulfonyl)amide <K—N(SO₂F)₂ (KFSA)>, and sodiumbis(fluorosulfonyl)amide <Na—N(SO₂F)₂ (NaFSA)>.

The molten salt is used in the state that the salt is impregnated intothe separator. The separator is a member for preventing the positiveelectrode and the negative electrode from contacting each other, and maybe a glass nonwoven fabric, a porous body of a porous resin, or someother. The above-mentioned positive electrode, negative electrode andseparator impregnated with the molten salt are laminated onto eachother, and the laminate is packaged into a case. The resultant is usedas a battery.

EXAMPLES

Hereinafter, the present invention will be described in more detail byway of examples; however, the present invention is not limited to theseexamples.

Example 1

(Formation of Conductive Layer)

The following was prepared as a urethane resin porous body: a urethanefoam having a porosity of 95%, about 50 pores (cells) per inch, and apore diameter (cell diameter) of about 550 μm, and a thickness of 1 mm.This was cut into a piece of 100 mm square. An aluminum film was formedon the surface of this polyurethane foam by a sputtering method to givea deposit amount of 10 g/m², thereby subjecting the foam to anelectrically conduction treatment.

The used urethane resin porous body was a porous body formed by thefollowing: when the foaming raw material of the polyurethane wascontinuously foamed in a sheet-form mold in the step of foaming thepolyurethane, the upper and lower planes of the mold were warmed to 60°C.

(Molten Salt Plating)

The urethane foam, the surface of which had the formed conductive layer,was used as a workpiece, and set to a tool having a power supplyingfunction. The foam was then put into a globe box containing an argonatmosphere and having a lower water content (dew point: −30° C. orlower), and immersed in a molten salt aluminum plating bath (33% by moleof EMIC/67% by mole of AlCl₃) of 40° C. temperature. The tool, to whichthe workpiece was set, was connected to the negative electrode side of arectifier, and an aluminum plate (purity: 99.99%) as a counter electrodewas connected to the positive electrode side. A direct current having acurrent density of 3.6 A/dm² was applied thereto for 90 minutes to platethe workpiece, thereby yielding an aluminum structural body wherein analuminum plating layer having a weight of 150 g/m² was formed on anysurface of the urethane foam. The bath was stirred with a stirrer usinga rotor made of Teflon (registered trade name). The current density wasa value obtained by making a calculation using the apparent area of theurethane foam.

(Decomposition of Resin Foam Shaped Body)

The aluminum structural body was immersed in a LiCl—KCl eutectic moltensalt of 500° C. temperature, and a negative potential of −1 V wasapplied thereto for 30 minutes. Bubbles were generated in the moltensalt by a decomposition reaction of the polyurethane. Thereafter, thestructural body was cooled to room temperature in the atmosphere, andthen washed with water to remove the molten salt. In this way, aresin-removed aluminum porous body 1 was yielded. The resultant aluminumporous body had continuous pores, and the porosity thereof was as highas that of the urethane foam used as the core member.

(Working of End of Aluminum Porous Body)

The resultant aluminum porous body was adjusted into a thickness of 0.96mm by a roller press. The porous body was then cut into a piece of 5 cmsquare.

For preparation for the welding, a SUS block (rod) of 5 mm width, as acompressing tool, and a hammer were used, and the SUS block was put ontoa region of the aluminum porous body that extended over a length of 5 mmfrom an end of one side of the body. The hammer was hit on the SUS blockto compress the porous body. In this way, a compressed region of 100 μmthickness was formed.

Thereafter, tab leads were welded thereto by spot welding underconditions described below:

<Welding Conditions>

Welding machine: Hi-Max 100, model No. YG-101UD, manufactured byPanasonic Corporation (a voltage of 250 V can be applied at most)

-   -   Capacity: 100 Ws, 0.6 kVa

Electrodes: copper electrodes having a diameter of 2 mm

Load: 8 kgf

Voltage: 140 V

<Tab Leads>

Material: aluminum

Size: a width of 5 mm, a length of 7 cm, and a thickness of 100 μm

Surface state: boehmite worked

An epoxy resin was filled into an opening in the resultant aluminumporous body 1, and the porous body was polished to create a crosssection. The cross section of the porous body was observed with amicroscope, and photographed. The photograph was divided into threeregions in the thickness direction of the porous body, and the regionswere named the region 1, the region 2 and the region 3, respectively. Byimage processing, the number of aluminum skeleton ribs of each of theregions was counted. The reciprocal thereof was calculated. Using thevalue of the region 2 as a standard, the ratio of the numerical value ofeach of the other regions thereto was gained.

The results are as shown in Table 1. The ratio of the reciprocal of thenumber of the aluminum skeleton ribs in the region 1 to that in theregion 2 was 1.19. In the same manner, the ratio of the reciprocal ofthe number of the aluminum skeleton ribs in the region 3 to that in theregion 2 was 1.19.

Example 2

An aluminum porous body 2 was formed in the same way as in Example 1except the use of a urethane resin having a thickness of 1.0 mm, 50cells, and a cell diameter of 550 μm, and formed by the following: whenthe foaming raw material of the polyurethane was continuously foamed ina sheet-form mold in the step of foaming the polyurethane, the upper andlower planes of the mold were cooled to 5° C.

In the same way as in Example 1, a cross section of the resultantaluminum porous body 2 was observed.

The results are as shown in Table 1. The ratio of the reciprocal of thenumber of the aluminum skeleton ribs in the region 1 to that in theregion 2 was 0.84. In the same manner, the ratio of the reciprocal ofthe number of the aluminum skeleton ribs in the region 3 to that in theregion 2 was 0.84.

Example 3

An aluminum porous body 3 was formed in the same way as in Example 1except the use of a urethane resin having a thickness of 1 mm, 50 cells,and a cell diameter of 550 μm, and formed by the following: when thefoaming raw material of the polyurethane was continuously foamed in asheet-form mold in the step of foaming the polyurethane, the upper planeof the mold was warmed to 60° C., and the lower plane was cooled to 5°C.

In the same way as in Example 1, a cross section of the resultantaluminum porous body 3 was observed. A microscopic photograph thereofwas divided into two regions in the thickness direction of the porousbody, and one of the regions was named the region 4, and the other theregion 5. In the same way as in Example 1, the reciprocal of the numberof aluminum skeleton ribs in each of the regions 4 and 5 was counted.

The results are as shown in Table 1. The ratio of the reciprocal of thenumber of the aluminum skeleton ribs in the region 4 to that in theregion 5 was 1.28.

Example 4

Aluminum porous bodies A and C were each formed in the same way as inExample 1 except the use of a urethane resin having a thickness of 0.33mm, 35 cells, and a cell diameter of 790 μm, and formed by thefollowing: when the foaming raw material of the polyurethane wascontinuously foamed in a sheet-form mold in the step of foaming thepolyurethane, the temperature of the upper and lower planes of the moldwas set to 25° C.

An aluminum porous body B was formed in the same way as in Example 1except the use of a urethane resin having a thickness of 0.34 mm, 55cells, and a cell diameter of 500 μm, and formed by the following: whenthe foaming raw material of the polyurethane was continuously foamed ina sheet-form mold in the step of foaming the polyurethane, thetemperature of the upper and lower planes of the mold was set to 25° C.

The resultant aluminum porous bodies A to C were laminated onto eachother to sandwich the aluminum porous body B between the aluminum porousbodies A and C. While pressure was applied thereto, the laminate washeated to integrate the porous bodies with each other. In this way, analuminum porous body 4 was yielded.

In the same way as in Example 1, a cross section of the resultantaluminum porous body 4 was observed.

The results are as shown in Table 1. The ratio of the reciprocal of thenumber of the aluminum skeleton ribs in the region 1 (the regionoriginating from the aluminum porous body A) to that in the region 2(the region originating from the aluminum porous body B) was 1.58. Inthe same manner, the ratio of the reciprocal of the number of thealuminum skeleton ribs in the region 3 (the region originating from thealuminum porous body C) to that in the region 2 was 1.58.

Example 5

Aluminum porous bodies D and F were each formed in the same way as inExample 1 except the use of a urethane resin having a thickness of 0.33mm, 55 cells, and a cell diameter of 500 μm, and formed by thefollowing: when the foaming raw material of the polyurethane wascontinuously foamed in a sheet-form mold in the step of foaming thepolyurethane, the temperature of the upper and lower planes of the moldwas set to 25° C.

An aluminum porous body E was formed in the same way as in Example 1except the use of a urethane resin having a thickness of 0.34 mm, 35cells, and a cell diameter of 790 μm, and formed by the following: whenthe foaming raw material of the polyurethane was continuously foamed ina sheet-form mold in the step of foaming the polyurethane, thetemperature of the upper and lower planes of the mold was set to 25° C.

The resultant aluminum porous bodies D to F were laminated onto eachother to sandwich the aluminum porous body E between the aluminum porousbodies D and F. While pressure was applied thereto, the laminate washeated to integrate the porous bodies with each other. In this way, analuminum porous body 5 was yielded.

In the same way as in Example 1, a cross section of the resultantaluminum porous body 5 was observed.

The results are as shown in Table 1. The ratio of the reciprocal of thenumber of the aluminum skeleton ribs in the region 1 (the regionoriginating from the aluminum porous body D) to that in the region 2(the region originating from the aluminum porous body E) was 0.63. Inthe same manner, the ratio of the reciprocal of the number of thealuminum skeleton ribs in the region 3 (the region originating from thealuminum porous body F) to that in the region 2 was 0.63.

Example 6

An aluminum porous body G was formed in the same way as in Example 1except the use of a urethane resin having a thickness of 0.5 mm, 35cells, and a cell diameter of 790 μm, and formed by the following: whenthe foaming raw material of the polyurethane was continuously foamed ina sheet-form mold in the step of foaming the polyurethane, thetemperature of the upper and lower planes of the mold was set to 25° C.

An aluminum porous body H was formed in the same way as in Example 1except the use of a urethane resin having a thickness of 0.5 mm, 55cells, and a cell diameter of 500 μm, and formed by the following: whenthe foaming raw material of the polyurethane was continuously foamed ina sheet-form mold in the step of foaming the polyurethane, thetemperature of the upper and lower planes of the mold was set to 25° C.

The resultant aluminum porous bodies G and H were laminated onto eachother. While pressure was applied thereto, the laminate was heated tointegrate the porous bodies with each other. In this way, an aluminumporous body 6 was yielded.

In the same way as in Example 1, a cross section of the resultantaluminum porous body 6 was observed. A microscopic photograph thereofwas divided into two regions in the thickness direction of the porousbody, and one of the regions was named the region 4, and the other theregion 5. In the same way as in Example 1, the reciprocal of the numberof aluminum skeleton ribs in each of the regions 4 and 5 was counted.

The results are as shown in Table 1. The ratio of the reciprocal of thenumber of the aluminum skeleton ribs in the region 4 (the regionoriginating from the aluminum porous body G) to that in the region 5(the region originating from the aluminum porous body H) was 1.58.

Comparative Example 1

An aluminum porous body 7 was formed in the same way as in Example 1except the use of a urethane resin having a thickness of 1.0 mm, 50cells, and a cell diameter of 550 μm, and formed by the following: whenthe foaming raw material of the polyurethane was continuously foamed ina sheet-form mold in the step of foaming the polyurethane, thetemperature of the upper and lower planes of the mold was set to 25° C.

In the same way as in Example 1, a cross section of the resultantaluminum porous body 7 was observed.

The results are as shown in Table 1. The ratio of the reciprocal of thenumber of the aluminum skeleton ribs in the region 1 to that in theregion 2 was 1.00. In the same manner, the ratio of the reciprocal ofthe number of the aluminum skeleton ribs in the region 3 to that in theregion 2 was 1.01.

TABLE 1 Cell diameter Number of Resin Foaming ratio (ratio cells poroustemperature between Cell diameter (cell- Cell body [° C.] reciprocals ofdistribution population diameter thickness Upper Lower numbers of inthickness Regions per inch) [μm] [mm] plane plane skeleton ribs)direction Example 1 1-3 50 550 1 60 60 Region 1: 1.19 1.19 Region 2:1.00 Region 3: 1.19 Example 2 1-3 50 550 1 5 5 Region 1: 0.84 0.84Region 2: 1.00 Region 3: 0.84 Example 3 4-5 50 550 1 60 5 Region 4: 1.281.28 Region 5: 1.00 Example 4 A 35 790 0.33 25 25 1.58 1.58 B 55 5000.34 25 25 1 C 35 790 0.33 25 25 1.58 Example 5 D 55 500 0.33 25 25 0.630.63 E 35 790 0.34 25 25 1 F 55 500 0.33 25 25 0.63 Example 6 G 35 7900.5 25 25 1.58 1.58 H 55 500 0.5 25 25 1 Comparative 1-3 50 550 1 25 25Region 1: 1.00 1 Example 1 Region 2: 1.00 Region 3: 1.01

-Production of Lithium Secondary Batteries-

As an active material, prepared was a lithium cobaltate powder (positiveelectrode active material) having an average particle diameter of 5 μm.This lithium cobaltate powder, acetylene black (conduction aid), andPVDF (binder) were mixed with each other at a ratio by mass percentageof 90:5:5. To this mixture was dropwise added N-methyl-2-pyrrolidone(organic solvent) to mix the solvent with the other components, therebyyielding a paste-like slurry mixture of positive electrode materials.

Next, this slurry mixture of positive electrode materials was filledinto aluminum porous body samples formed by Examples 1 to 6, andComparative Example 1 to make the individual positive electrode mixtureamounts equal to each other. Thereafter, the samples were dried at 100°C. for 40 minutes to remove the organic solvent, and further the sampleswere each compressed by a roller press (roller gap: 0.2 mm) to yieldpositive electrode samples 1 to 7. Each of the positive electrodes had athickness of 500 μm and a capacity per area of 10 mAh/cm².

The positive electrode samples 1 to 7 were each used to produce anelectrolyte type lithium secondary battery as follows:

As a positive electrode, use was made of an electrode obtained bypunching out each of the samples 1 to 7 into a diameter of 14 mm. As anegative electrode, use was made of a lithium metal foil (diameter: 15mm, and thickness: 500 μm). The positive electrode (positive electrodesample) and the negative electrode were laminated onto each other tointerpose a separator made of polypropylene therebetween. This waspackaged into a coin type battery case having a positive electrode canand a negative electrode can each made of stainless steel. An organicelectrolyte was then injected into the battery case. The used organicelectrolyte was a solution wherein LiClO₄ was dissolved in a mixedorganic solvent of propylene carbonate and 1,2-dimethoxyethane (ratio byvolume: 1:1) to give a concentration of 1% by mole. After the injectionof the organic electrolyte, a gasket made of a resin was sandwichedbetween the positive electrode can and the negative electrode can, andthen these cans were caulked with each other to seal the inside toproduce a coin type electrolyte type lithium secondary battery.

The battery for evaluation was produced about each of the positiveelectrode samples. When any one of the positive electrode samples wasused, no leaf spring was inserted between the positive electrode sampleand the positive electrode can.

The electrolyte type lithium secondary batteries using the positiveelectrode samples 1 to 7, respectively, were evaluated as follows:

(Rate Characteristic Evaluation)

In this evaluation, each of some of the batteries was subjected tocharge/discharge cycles wherein the charge/discharge current was 3 mAand the voltage was set into the range of 4.2 to 2.0 V, and then thedischarge capacity was measured. The battery was charged at a chargecurrent of 3 mA, and then the discharge capacity thereof was measured atrespective discharge currents of 10 mA and 50 mA. The ratio of each ofthe resultant values to the discharge capacity at 3 mA was examined.

As shown in Table 2, it is understood that Examples 1 and 4 were betterin rate characteristic (current collecting performance) than ComparativeExample 1.

(Cycle Characteristic Evaluation)

Furthermore, a charge/discharge cycle test was made to examine thelifespan of each of some of the batteries. In this evaluation,charge/discharge cycles were made wherein the charge/discharge currentwas 3 mA and the voltage was set into the range of 4.2 to 2.0 V to makea change in the discharge capacity. After 100 and 1000 cycles of thecharge/discharge cycles, the capacity was checked, and then the batterywas dismantled to observe the inside. The discharge capacity isrepresented by the percentage of the checked capacity in the capacity inthe first discharging as a standard.

As shown in Table 2, it is understood that Example 2 or 5 was better incycle life (holding performance of the active material) than ComparativeExample 1. Additionally, the batteries after the 1000 cycles weredismantled, and the respective insides thereof were observed. As aresult, in Comparative Example 1, the active material dropped away fromthe electrodes to be liberated in the electrolyte. It is understood fromthis matter that in Example 2 or 5, the active material was morestrongly held so that an advantage in cycle life was produced.

(Bending Workability)

Aluminum porous bodies 3 as yielded in Example 3, as well as the bodies6 and 7 as yielded in Example 6 and Comparative Example 1, were eachused to yield a negative electrode sample in the same way as used toproduce the positive electrode samples except that a lithium titanatepowder having an average particle diameter of 5 μm was used as an activematerial.

Positive electrode samples 3, 6 and 7 were each cut into a piece 45 mmwide and 230 mm long. An aluminum lead wire was welded to the cut piece.In the same way, the negative electrode samples 3, 6 and 7, were eachcut into a piece 45 mm wide and 280 mm long. Separators were each cutinto a piece 50 mm wide and 500 mm long, and the piece was twice-folded.One of the positive electrodes 3 was sandwiched between the half regionsof one of the separator pieces, and the resultant was put onto one ofthe negative electrodes 3. The workpiece was wound to make the negativeelectrode exposed outward. In this way, a group of the electrodes wasyielded. In the same way, use was made of a pair of one of the positiveelectrodes 6 and one of the negative electrodes 6, and a pair of one ofthe positive electrodes 7 and one of the negative electrodes 7 to yieldwound electrode groups. In Example 3 or 6, the winding was performed toface the electrode having a larger cell diameter outward.

These electrode groups were each inserted into a negative electrodeelectrolytic tank can for a 18650 cylindrical battery, and then the leadwire of the positive electrode, and a positive electrode lid to which aresin gasket was attached were welded to each other. An electrolyte wasinjected thereinto, the solution being a solution wherein LiClO₄ wasdissolved in a mixed organic solvent of propylene carbonate and1,2-dimethoxyethane (ratio by volume: 1:1) to give a concentration of 1%by mole. The positive electrode lid and the negative electrode can werecaulked with each other to seal the inside, thereby yielding acylindrical lithium secondary battery 18 mm in diameter and 65 mm inheight. Thereafter, in order to evaluate the bending workability of theelectrodes, the battery was examined about the generation percentage ofshort circuit after the winding/fabrication.

As shown in Table 2, it is understood that Example 3 or 6 was lower inshort circuit generation percentage after the winding than ComparativeExample 1.

TABLE 2 Rate characteristic Cycle life (active Short circuit (currentcollecting material holding generation performance) performance)percentage [%] Discharge Discharge After After after winding capacity atcapacity at 100 1000 (bending 10 mA 50 mA cycles cycles workability)Example 1 101 92 — — — Example 2 — — 100 89 — Example 3 — — — — 0.3Example 4 100 96 — — — Example 5 — — 101 95 — Example 6 — — — — 0.1Comparative 100 87 100 79 1.3 Example 1

The following will describe examples other than the above-mentionedexamples.

Example 7 Formation of Aluminum Porous Body

As urethane resin porous bodies, prepared were a polyurethane foam(urethane foamed body) having a porosity of about 97%, a pore diameter(cell diameter) of about 200 μm, and a thickness of about 500 μm, and apolyurethane foam (urethane foamed body) having a porosity of about 97%,a pore diameter (cell diameter) of about 400 μm, and a thickness ofabout 500 μm. These urethane foams were substantially even in celldiameter in the thickness direction.

Next, about each of the urethane foams, pure aluminum was molten andevaporated to form an aluminum layer on any surface of the urethane foamby a vacuum vapor deposition. Conditions for the vacuum deposition wereas follows: the vacuum degree was set to 1.0×10⁻⁵ Pa; the temperature ofthe urethane foam, on which the film was to be formed, to roomtemperature; and the distance between the evaporation source and theurethane foam, to 300 mm. After the formation of the aluminum layer onthe surface of each of these urethane foamed bodies, an SEM was used toobserve the urethane foamed body (aluminum structural body), wherein thealuminum layer was formed on the resin surface. As a result, thethickness of the aluminum layer was 15 μm.

The aluminum structural bodies were each immersed in a LiCl—KCl eutecticmolten salt of 500° C. temperature, and further in the state a negativevoltage was applied to the aluminum layer for 30 minutes to make thepotential of the aluminum layer into −1 V relatively to the reductionpotential of aluminum. At this time, it was recognized that bubbles weregenerated in the molten salt. It is presumed that this was based onthermal decomposition of the polyurethane.

Next, the skeleton (aluminum porous body) yielded in the above-mentionedstep, which was made of the aluminum yielded after each of the urethanefoamed bodies was thermally decomposed, was cooled to room temperaturein the atmosphere, and then washed with water to remove the molten saltadhering to the surface. In this way, two types of aluminum porousbodies were finished.

Of the produced aluminum porous bodies, one (wherein the resin body ofabout 200 μm cell diameter was used) had a porosity of 97%, a celldiameter of 200 μm and a thickness of 500 μm, and the other (wherein theresin body of about 400 μm cell diameter was used) had a porosity of97%, a cell diameter of 400 μm and a thickness of 500 μm. The aluminumporous bodies were each observed with an SEM. As a result, its poreswere continuous to each other, and no closed pores were observed.Furthermore, the surface of each of the aluminum porous bodies wasquantitatively analyzed by EDX at an accelerating voltage of 15 kV. As aresult, no oxygen peak was observed. In other words, no oxygen wasdetected. Accordingly, the oxygen content in the surface of each of thealuminum porous bodies was below the detection limit thereof accordingto EDX, that is, 3.1% by mass or less. The instrument used in theanalysis was “EDAX Phoenix, model type: HIT22 136-2.5” manufactured byEDAX Inc.

Furthermore, the aluminum porous bodies were used to produce abilayered-structure aluminum porous body 8, and a trilayered-structurealuminum porous body 9, respectively. Specifically, thebilayered-structure aluminum porous body 8 was produced by laminatingthe porous body of 200 μm cell diameter and the porous body of 400 μmcell diameter onto each other, and bonding the porous bodies by spotwelding while their surfaces were pushed onto each other. Separately,the trilayered-structure aluminum porous body 9 was produced bypreparing one aluminum porous body of 200 μm cell diameter, preparingtwo porous bodies of 400 μm cell diameter, laminating the porous bodiesof 400 μm cell diameter onto both surfaces of the porous body of 200 μmcell diameter, respectively, and bonding the porous bodies by spotwelding while their surfaces were pushed onto each other. In otherwords, the bilayered-structure aluminum porous body 8 had alarge-cell-diameter region and a small-cell-diameter region in thethickness direction, and the trilayered-structure aluminum porous body 9had a large-cell-diameter region, a small-cell-diameter region, andanother large-cell-diameter region in turn in the thickness direction.

Comparative Example 2

For comparison, prepared were two types of polyurethane foams (urethanefoamed bodies) having a porosity of about 97%, a pore diameter (celldiameter) of about 200 μm, and respective thicknesses of 1000 μm and1500 μm. In the same way as used to produce the aluminum porous bodiesof Example 7, aluminum porous bodies 10 and 11 having differentthicknesses were produced. Each of the aluminum porous bodies 10 and 11had a porosity of 97% and a cell diameter of 200 μm, and had, in thesurface thereof, an oxygen content of 3.1% by mass or less.

(Production of Electrodes for Nonaqueous Electrolyte Batteries)

An active material was filled into each of the aluminum porous bodies 8to 11 to produce a positive electrode for a lithium secondary battery.

In the production, prepared was a LiCoO₂ powder (positive electrodeactive material) having an average particle diameter of 10 μm. ThisLiCoO₂ powder, AB (conduction aid), and PVDF (binder) were mixed witheach other at a ratio by mass percentage of 90:5:5. To this mixture wasdropwise added N-methyl-2-pyrrolidone (organic solvent) to mix thesolvent with the other components, thereby yielding a paste-like slurrymixture of positive electrode materials. Next, each of the aluminumporous bodies was impregnated into this slurry mixture of positiveelectrode materials to fill the aluminum porous body with the positiveelectrode mixture. Thereafter, the aluminum porous body was dried at100° C. for 40 minutes to remove the organic solvent. Next, the aluminumporous body filled with the positive electrode mixture was subjected tocompression-press forming by a roller press. In this way, a positiveelectrode material using each of the aluminum porous bodies wasfinished.

Finally, from each of the produced positive electrode materials, asample of 15 mm diameter was punched out. The resultant samples, whichwere yielded by punching out the aluminum porous bodies 8 to 11, werenamed positive electrode samples 8 to 11, respectively. The aluminumporous bodies 8 and 10 of 1000 μm thickness were each compressed into athickness of 500 μm, and designed to set the capacity density per unitarea, which was obtained from the mass of the positive electrode activematerial, to 10 mAh/cm². The aluminum porous bodies 9 and 11 of 1500 μmthickness were each compressed into a thickness of 750 μm, and designedto set the capacity density per unit area, which was obtained from themass of the positive electrode active material, to 15 mAh/cm².

Next, the positive electrode samples 8 to 11 were used to produceelectrolyte type lithium secondary batteries, respectively, and evaluatethe positive electrode samples. The evaluating batteries were producedas follows:

About each of the positive electrode samples 8 and 10, a lithium (Li)metal foil (diameter: 15 mm, and thickness: 500 μm) was used as itsnegative electrode. The positive electrode (positive electrode sample)and the negative electrode were laminated onto each other to interpose aseparator (thickness: 25 μm) made of polypropylene therebetween. At thistime, about the positive electrode sample 8, the positive electrode wasarranged to face, toward the negative electrode, the surface of thelarge-pore-diameter side (large-cell-diameter region side) of thealuminum porous body. A terminal member was attached to each of theelectrodes, and the resultant was immersed in an organic electrolyte putin a vessel. In this way, evaluating batteries were produced. The usedorganic electrolyte was a solution wherein LiPF₆ was dissolved in amixed organic solvent of ethylene carbonate (EC) and diethyl carbonate(DEC) (ratio by volume: 1:1) to give a concentration of 1 M (mol/L).

About each of the positive electrode samples 9 and 11, a negativeelectrode, separators and an organic electrolyte used therein were thesame as about the positive electrode samples 8 and 10. These werelaminated in the following order: negative electrode/separator/positiveelectrode (positive electrode sample)/separator/negative electrode. Atthis time, the positive electrode samples 9 and 11 were arranged toface, toward the negative electrode, the surface of thelarge-pore-diameter side (large-cell-diameter region side) of thealuminum porous body. A terminal member was attached to each of theelectrodes, and the resultant was immersed in an organic electrolyte putin a vessel. In this way, evaluating batteries were produced.

The evaluating batteries using the respective positive electrode sampleswere evaluated as follows: In the evaluation, charge/discharge cycleswere made at cutoff voltages of 4.2 to 3.0 V and respective currentdensities of 0.2 C and 2 C. At this time, the batteries were eachmeasured about the initial discharge capacity. From the measured initialdischarge capacity, the discharge capacity per unit mass of the positiveelectrode active material was calculated by conversion. The respectivedischarge capacities of the batteries are shown in Table 3.

TABLE 3 Positive Discharge capacity Discharge capacity electrode Alporous body (mAh/g) at current (mAh/g) at current sample (structure)density of 0.2 C density of 2 C 8 Bilayered 120 110 9 Trilayered 120 11010 Monolayered 120 90 11 Monolayered 120 90

As shown in Table 3, about the positive electrode samples 8 to 11,wherein the aluminum porous bodies 8 to 11 were used as their currentcollectors, respectively, a difference was hardly found out between thedischarge capacities at the low-rate-discharge, wherein the currentdensity was low. However, at the high-rate-discharge, wherein thecurrent density was high, the positive electrode samples 8 and 9,wherein the aluminum porous bodies 8 and 9 were used as their currentcollectors, respectively, were higher in discharge capacity than thepositive electrode samples 10 and 11, wherein the aluminum porous bodies10 and 11 were used as their current collectors, respectively. Thus, itis understood that aluminum porous bodies 8 and 9 can improve adischarge characteristic of a battery.

The reason therefor would be as follows: (i) the aluminum porous bodieseach have the large-cell-diameter region(s) and the small-cell-diameterregion in the thickness direction, so that the permeability of theorganic electrolyte is high and the availability ratio of the activematerial is high. Additionally, in each of the positive electrodesamples 8 to 11, the oxygen content in the aluminum porous body surfacefunctioning as the current collector is 3.1% by mass or less, which isvery small; thus, donation and reception of electrons are rapidlyattained between the porous body and the active material.

The above has described the present invention on the basis ofembodiments thereof; however, the present invention is not limited tothe embodiments. Within the scope of the present invention and any scopeequivalent thereto, various modifications may be added to theembodiments.

INDUSTRIAL APPLICABILITY

The use of the three-dimensional net-like aluminum porous body of thepresent invention as a base of an electrode makes it possible to improvethe current collecting performance of a central region in the thicknessdirection of the electrode, and the availability ratio of the activematerial inside the electrode. Furthermore, the use makes it possible toimprove the electrode in holding performance of the active material, andin windability. Thus, the aluminum porous body of the present inventioncan be used suitably as a base in industrial and continuous productionof electrodes for, for example, nonaqueous electrolyte batteries (suchas lithium batteries), and nonaqueous electrolyte condensers.

REFERENCE SIGN LIST

1: resin porous body

2: conductive layer

3: aluminum plating layer

21 a and 21 b: plating tank

22: band-form resin

23 and 28: plating bath

24: cylindrical electrode

25 and 27: positive electrode

26: electrode roller

32: compressing tool

33: compressed region

34: aluminum porous body

35: rotatable roller

36: roller rotation axis

41: winding-back roller

42: compressing roller

43: compressing/welding roller

44: filling roller

45: drying machine

46: compressing roller

47: cutting roller

48: winding-up roller

49: lead supplying roller

50: slurry supplying nozzle

51: slurry

60: lithium battery

61: positive electrode

62: negative electrode

63: electrolyte layer

64: positive electrode layer (positive electrode body)

65: current collector of positive electrode

66: negative electrode layer

67: negative electrode current collector

121: positive electrode

122: negative electrode

123: separator

124: holding plate

125: spring

126: pressing member

127: case

128: positive electrode terminal

129: negative electrode terminal

130: lead wire

141: polarizable electrode

142: separator

143: organic electrolyte

144: lead wire

145: case

The invention claimed is:
 1. A planar three-dimensional network aluminumporous body, for a current collector, comprising: a first cell-diameterregion in a thickness direction of the porous body, the firstcell-diameter region having a first cell diameter of the porous body inthe thickness direction, the first cell diameter being based on areciprocal number of skeleton ribs in the first cell-diameter region,and the first cell diameter being defined as an average given by: (aunit length)/(a first number of cells), and a second cell-diameterregion in the thickness direction of the porous body, the secondcell-diameter region having in the thickness direction a second celldiameter of the porous body that is larger than the first cell diameter,the second cell diameter being based on a reciprocal number of skeletonribs in the second cell-diameter region, and the second cell diameterbeing defined as an average given by: (the unit length)/(a second numberof cells), wherein a plurality of the skeleton ribs in the firstcell-diameter region and the second cell-diameter region are hollow andhave a uniform thickness aluminum layer, and a cross section in thethickness direction of the porous body has three regions laminated toeach other including a region 1 of the first cell diameter, a region 2of the second cell diameter, and a region 3 of the first cell diameter,in order, and a ratio of the average cell diameter of the region 1 andthe region 3 to the cell diameter of the region 2 is 0.9 or less.
 2. Theplanar three-dimensional network aluminum porous body according to claim1, wherein an oxygen content in a surface of the porous body is 3.1% bymass or less.
 3. The planar three-dimensional network aluminum porousbody according to claim 1, wherein when the porous body is divided inthe thickness direction thereof into a large-cell-diameter region havinga large cell diameter and a small-cell-diameter region having a smallercell diameter than this large cell diameter, the cell diameter of thelarge-cell-diameter region is 300 μm or more and 600 μm or less.
 4. Theplanar three-dimensional network aluminum porous body according to claim1, wherein when the porous body is divided in the thickness directionthereof into a large-cell-diameter region having a large cell diameterand a small-cell-diameter region having a smaller cell diameter thanthis large cell diameter, the cell diameter of the small-cell-diameterregion is 50 μm or more and 300 μm or less.
 5. An electrode wherein theplanar three-dimensional network aluminum porous body as recited inclaim 1 is used.
 6. A nonaqueous electrolyte battery wherein theelectrode as recited in claim 5 is used.
 7. A capacitor using anonaqueous electrolyte wherein the electrode as recited in claim 5 isused.